Understanding

inher itance
What controls traits?

• Mendel concluded that two factors control
each trait.

• He also concluded that they can be
domin...
What controls traits?

chromosomes

• Inside each cell is a nucleus that has

chromosomes. Chromosomes contain
genetic inf...
What controls traits?

chromosomes

• Each cell in an offspring contains
chromosomes from both parents.

• These chromosom...
What controls traits?

genes & alleles

• Each chromosome can
have information
about 100’s or 1000’s
of traits.

• A gene ...
What controls traits?

genes & alleles

• An offspring inherits two genes for each
trait, one from each parent.

• The gen...
What controls traits?

genes & alleles

• Another example of a trait and its forms
is having dimples or not having dimples...
What controls traits?

genes & alleles

• The different forms of a gene are called
alleles.
What controls traits?

genot ype & phenot ype
• Geneticists call how a trait appears, or is

expressed, the trait’s phenot...
What controls traits?

genot ype & phenot ype
• Mendel concluded that there were two

alleles that controlled the phenotyp...
What controls traits?

genot ype & phenot ype
What controls traits?

genot ype & phenot ype
• Scientists use symbols to represent the
alleles in a genotype.

• Uppercas...
What controls traits?

genot ype & phenot ype
What controls traits?

homoz ygous & het er oz ygous
homozygous:

heterozygous:

RR
rr

Rr
modeling inheritance

• Plant breeders and animal breeders use

two tools to help them predict how often
traits will appea...
modeling inheritance

Punnet t Square
Pedigree
modeling inheritance

Punnet t Squar es

• If the genotypes of the parents are

known, then the different genotypes and
ph...
modeling inheritance

Punnet t Squar es
modeling inheritance

Pedigr ees

• A pedigree shows phenotypes of

genetically related family members.

• It can also hel...
modeling inheritance

Pedigr ees

• Let’s look at the phenotypes of the
children.....
complex patterns of inheritance

t ypes of dominance:

• Mendel studied traits influenced by only
one gene with two allele...
complex patterns of inheritance

t ypes of dominance:
incomplete dominance

• Alleles show incomplete dominance when

the ...
complex patterns of inheritance

t ypes of dominance:
incomplete dominance
complex patterns of inheritance

t ypes of dominance:
incomplete dominance
complex patterns of inheritance

t ypes of dominance:
codominance

• When both alleles can be observed in a
phenotype, thi...
complex patterns of inheritance

t ypes of dominance:

codominance
• For example, if a
cow inherits the
allele for white
c...
complex patterns of inheritance

mul t iple alleles

• Unlike the genes in Mendel’s pea plants,

some genes have more than...
complex patterns of inheritance

mul t iple alleles

• In the pea plants there were two possible
phenotypes, ie round pea ...
complex patterns of inheritance

mul t iple alleles

• The IA and IB alleles are codominant to

each other, but they both ...
complex patterns of inheritance

mul t iple alleles
complex patterns of inheritance

polygenic inher i tance

• Mendel concluded that only one gene

determined each trait. We...
complex patterns of inheritance

polygenic inher i tance
complex patterns of inheritance

polygenic inher i tance

• Because several genes determine a trait,
many alleles affect t...
complex patterns of inheritance

polygenic inher i tance
genes and the environment

• Genes are not the only factors that can
affect phenotypes. An organism’s
environment can also...
genes and the environment

• The flower color of one type of hydrangea
is determined by the soil in which the
hydrangea pl...
genes and the environment

• Himalayan rabbits have

alleles for dark-coloured
fur, which is only
displayed at lower
tempe...
genes and the environment

• For humans, healthful choices can also
affect phenotype.

• Many genes affect a person’s chan...
recessive genetic disorders

• Disorders

caused by
recessive genes.
You must have
both recessive
alleles in order
to have...
recessive genetic disorders
sex-linked disorders

• Red-green colour blindness is a recessive
sex-linked disorder.

• It occurs on the X chromosome.

...
sex-linked disorders
recessive genetic disorders
Understanding Inheritance
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Understanding Inheritance

  1. 1. Understanding inher itance
  2. 2. What controls traits? • Mendel concluded that two factors control each trait. • He also concluded that they can be dominant or recessive. • One factor comes from the egg cell and one factor comes from the sperm cell. • What are these factors? How are they passed from parents to offspring?
  3. 3. What controls traits? chromosomes • Inside each cell is a nucleus that has chromosomes. Chromosomes contain genetic information that controls traits. • What Mendel called “factors” are parts of chromosomes. We know them as genes.
  4. 4. What controls traits? chromosomes • Each cell in an offspring contains chromosomes from both parents. • These chromosomes exist in pairs — one chromosome from each parent.
  5. 5. What controls traits? genes & alleles • Each chromosome can have information about 100’s or 1000’s of traits. • A gene is a section on a chromosome that has genetic information for one trait.
  6. 6. What controls traits? genes & alleles • An offspring inherits two genes for each trait, one from each parent. • The genes can be the same or different, such as purple or white for pea flower color. XX
  7. 7. What controls traits? genes & alleles • Another example of a trait and its forms is having dimples or not having dimples.
  8. 8. What controls traits? genes & alleles • The different forms of a gene are called alleles.
  9. 9. What controls traits? genot ype & phenot ype • Geneticists call how a trait appears, or is expressed, the trait’s phenotype. • A person’s eye color is an example of phenotype. The trait of eye color can be expressed as blue, brown, green, or other colors.
  10. 10. What controls traits? genot ype & phenot ype • Mendel concluded that there were two alleles that controlled the phenotype of each trait. • The two alleles that control the phenotype of a trait are called the trait’s genotype. • You cannot see an organism’s genotype. But you can make guesses about a genotype based on its phenotype.
  11. 11. What controls traits? genot ype & phenot ype
  12. 12. What controls traits? genot ype & phenot ype • Scientists use symbols to represent the alleles in a genotype. • Uppercase letters represent dominant alleles and lowercase letters represent recessive alleles. • The dominant allele, if present, is written first.
  13. 13. What controls traits? genot ype & phenot ype
  14. 14. What controls traits? homoz ygous & het er oz ygous homozygous: heterozygous: RR rr Rr
  15. 15. modeling inheritance • Plant breeders and animal breeders use two tools to help them predict how often traits will appear in offspring. • These tools, Punnett squares and pedigrees, can be used to predict and identify traits among genetically related individuals.
  16. 16. modeling inheritance Punnet t Square Pedigree
  17. 17. modeling inheritance Punnet t Squar es • If the genotypes of the parents are known, then the different genotypes and phenotypes of the offspring can be predicted. • A Punnett square is a model used to predict possible genotypes and phenotypes of offspring.
  18. 18. modeling inheritance Punnet t Squar es
  19. 19. modeling inheritance Pedigr ees • A pedigree shows phenotypes of genetically related family members. • It can also help determine genotypes.
  20. 20. modeling inheritance Pedigr ees • Let’s look at the phenotypes of the children.....
  21. 21. complex patterns of inheritance t ypes of dominance: • Mendel studied traits influenced by only one gene with two alleles. • We know now that not all traits are inherited this way. Some traits have more complex inheritance patterns.
  22. 22. complex patterns of inheritance t ypes of dominance: incomplete dominance • Alleles show incomplete dominance when the offspring’s phenotype is a blend of the parents’ phenotypes. • Here is an example with 4 o’clock flowers.
  23. 23. complex patterns of inheritance t ypes of dominance: incomplete dominance
  24. 24. complex patterns of inheritance t ypes of dominance: incomplete dominance
  25. 25. complex patterns of inheritance t ypes of dominance: codominance • When both alleles can be observed in a phenotype, this type of interaction is called codominance.
  26. 26. complex patterns of inheritance t ypes of dominance: codominance • For example, if a cow inherits the allele for white coat color from one parent and the allele for red coat color from the other parent, the cow will have both red and white hairs.
  27. 27. complex patterns of inheritance mul t iple alleles • Unlike the genes in Mendel’s pea plants, some genes have more than two alleles, or multiple alleles. • Human ABO blood type is an example of a trait that is determined by multiple alleles. • There are three alleles for the ABO blood type—IA, IB, and i.
  28. 28. complex patterns of inheritance mul t iple alleles • In the pea plants there were two possible phenotypes, ie round pea or wrinkled pea. • The way the alleles combine for blood types, results in one of four blood types—A, B, AB, or O.
  29. 29. complex patterns of inheritance mul t iple alleles • The IA and IB alleles are codominant to each other, but they both are dominant to the i allele. • Even though there are multiple alleles, a person inherits only two of these alleles, one from each parent.
  30. 30. complex patterns of inheritance mul t iple alleles
  31. 31. complex patterns of inheritance polygenic inher i tance • Mendel concluded that only one gene determined each trait. We now know that more than one gene can affect a trait. • Polygenic inheritance occurs when multiple genes determine the phenotype of a trait.
  32. 32. complex patterns of inheritance polygenic inher i tance
  33. 33. complex patterns of inheritance polygenic inher i tance • Because several genes determine a trait, many alleles affect the phenotype even though each gene has only two alleles. • Therefore, polygenic inheritance has many possible phenotypes. • Eye color, height, weight and skin color are all examples of traits that are determined by polygenic inheritance.
  34. 34. complex patterns of inheritance polygenic inher i tance
  35. 35. genes and the environment • Genes are not the only factors that can affect phenotypes. An organism’s environment can also affect its phenotype. • For example, the flower color of one type of hydrangea is determined by the soil in which the hydrangea plant grows. • Acidic soil produces blue flowers. Basic soil produces pink flowers.
  36. 36. genes and the environment • The flower color of one type of hydrangea is determined by the soil in which the hydrangea plant grows. • Acidic soil produces blue flowers. Basic soil produces pink flowers.
  37. 37. genes and the environment • Himalayan rabbits have alleles for dark-coloured fur, which is only displayed at lower temperatures. • The fur in areas further from the rabbit’s body heat i.e. nose, ears, feet, are therefore darkly coloured.
  38. 38. genes and the environment • For humans, healthful choices can also affect phenotype. • Many genes affect a person’s chances of having heart disease. • However, what a person eats and the amount of exercise he or she gets can influence whether heart disease will develop.
  39. 39. recessive genetic disorders • Disorders caused by recessive genes. You must have both recessive alleles in order to have the disorder.
  40. 40. recessive genetic disorders
  41. 41. sex-linked disorders • Red-green colour blindness is a recessive sex-linked disorder. • It occurs on the X chromosome. XX XX XX XY XY female not color blind female not color blind male not color blind female color blind male color blind
  42. 42. sex-linked disorders
  43. 43. recessive genetic disorders

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