1. Traits are passed or inherited from one generation to the next.• Your genetic instructions are located in the nucleus of every cell, stored within chromosomes.
How will your traits be passed on to your future children?• Fathers pass genetic instructions to offspring through sperm cells.• Mothers pass genetic instructions to offspring through egg cells.
2. Genes control the traits of an organism.•No, not THAT Gene!
2. Genes control the traits of an organism.• A gene is a section of a chromosome, that codes for a specific trait.• Chromosomes are made of tightly wound strands of DNA
3. Organisms inherit genes in pairs, one from each parent.• Human sex cells (sperm or egg) contain 23 chromosomes each.• When the egg is fertilized, the embryo will have 46 chromosomes in each of its cells, which is the correct number of chromosomes for a human.
Sexual Reproduction (2 parents) creates unique offspring.• In plants, male chromosomes are passed through pollen grains to female egg cells. Once fertilized, these eggs will develop into seeds.• The new plants will receive a combination of traits from both parents.
4. Some genes are dominant, while others are recessive.• “Stronger” traits are called dominant.• “Weaker” traits are called recessive.• Geneticists use symbols (letters) to represent the different forms of a gene.
Dominant traits arerepresented by a capital letter.• Yellow seeds are dominant…….. Y
Recessive genes (for the same trait) are represented by THE SAME letter, but it is lower case .Green seeds are recessive………. yDominant (yellow) = YRecessive (green) = y
Pea Plant Genotype • In pea plants, tall is dominant over short. The letter used to represent the tall gene is T (BIG T). • The short gene isTall =T represented by tShort = t (little t).
In humans, brown eyes are dominant over blue. Brown = B Blue = b
5. Dominant genes hide recessive geneswhen an organism inherits both. • Y + y = yellow seeds (yellow is dominant) • T + t = tall plant (tall is dominant) • B+ b = brown eyes (brown is dominant)
A PUREBRED organism has two of the same genes for a trait. • TT = purebred TALL • tt = purebred SHORT • This genotype is also called HOMOZYGOUS
A HYBRID organism has two different genes for a trait.• Tt = hybrid TALL (tall is dominant)• This genotype is also called HETEROZYGOUS
Will a hybrid human with the genes Bb have brown or blue eyes?• Bb = Brown eyes• The dominant gene (brown), will be expressed in a hybrid.
Why must all blue eyed people be PUREBRED for that trait?• If the dominant gene is present, it will always be expressed.• The only possible gene combination for blue eyes is bb
6. Some genes are neither dominant nor recessive. These genes show incomplete dominance.• If an organism shows INCOMPLETE DOMINANCE for a trait, the hybrid will show a blend of the two traits.
Human Hair Texture• Because neither curly nor straight hair is recessive, no lower case letters are used.• CC = curly hair• CS = wavy hair• SS = straight hair
These basic laws of inheritance control the traits of all living organisms on Earth.
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