Genetics Grade 9 Science, DNA, Chromosomes - organization of DNA

1. DNA, Genes, and Chromosomes
The Instructions for Life

2. Inheritance
 Process by which genetic information is
passed on from parents to offspring
Genetics
 Branch of Biology concerned with the
study of genes, genetic variation and
heredity of organism.

3. Gene
 Segment of DNA that has the information
(the code) for a protein.
 A single molecule of DNA has thousands
of genes.

4.  Chromosomes are the form DNA becomes
in the nucleus when the cell is preparing to
divide.
 Humans have 46 chromosomes.
 One set of 23 chromosomes from mother.
 One set of 23 chromosomes from father.
Chromosomes

5. Types of Chromosomes:
 Autosomes: Body chromosomes or non
sex chromosomes (humans have 44 or
22 pairs)
 Sex Chromosomes: XX or XY (23rd
pair for humans) determines the sex of
the offspring

6. Each species has a specific number of
chromosomes.
Diploid (2n) : two sets of chromosomes
 Found in all the non-sex cells or autosomes
of an organism's body
Haploid (n) one set of chromosomes.
 Only sperm and egg cells(sex cells) have
the haploid number.

7. Chromatid
 Two exact copies of a chromosome that are
connected together.
 The point where they are connected near
the middle is called the centromere.
 Chromatids are made when new cells are
going to be made.

8. DNA
 DNA is commonly referred to as
deoxyribonucleic acid.
 The nucleic acid has a phosphate backbone
with bases such as adenine, cytosine,
guanine, and thymine, while the
deoxyribose portion contains pentose
sugar.

10. Genes
 Any difference between cells individual
organisms or groups of organism of any
species.
Variation
 Unit of heredity, a section of DNA that
codes for specific traits.

11. Genotype VS. Phenotype
Genetic makeup of
organism
Physical traits of organism

12. WHO IS GREGOR MENDEL?

13. Pea Plant
Why Pea Plant?

15. Results of Mendel’s Works

16. Mendelian Genetics
 Law of Dominance
This is also called Mendel’s first law of
inheritance. According to the law of
dominance, hybrid offspring will only inherit
the dominant trait in the phenotype.

17. Punnett Square
 A graphical representation of the possible
genotypes of an offspring arising from a
particular cross.
 Named after Reginald Punnet

18. DOMINANT TRAITS
 Gene or factor that makes another gene
RECESSIVE TRAITS
 Gene or factor that is masked by dominant
gene
ALLELES
 Gene that are found in the same location of
chromosomes

19. Mendelian Genetics
 Law of Segregation
The law of segregation states that during
the production of gametes, two copies of
each hereditary factor segregate so that
offspring acquire one factor from each
parent.

21. Mendelian Genetics
 Law of Independent Assortment
Also known as Mendel’s second law of
inheritance, the law of independent assortment
states that a pair of traits segregates
independently of another pair during
gamete formation

22. MONOHYBRID VS.
DIHYBRID
What is difference between Monohybrid and
dihybrid cross?
 A monohybrid cross is defined as the
cross happening in the F1 generation
offspring of parents differing in one trait
only. A dihybrid cross is a cross happens
F1 generation offspring of differing in two
traits.

24. DIHYBRID CROSS

25. Practice task
 In rabbits, gray hair is dominant to white
hair. Also in rabbits, black eyes are
dominant to red eyes. These letters
represent the genotypes of the rabbits:
GG- Gray hair BB- Black eyes
Gg – Hair Bb – Black eyes
Gg – White hair bb – red eyes

26. PRACTICE TASKS.
 1. A male rabbit with the genotype GGbb is
crossed with a female rabbit with the
genotype ggBb. Fill it out and determine
the phenotypes and proportions in the
offspring.
 A male rabbit with the genotype GgBb is
crossed with a female rabbit with the
genotype GgBb. Fill it out and determine
the phenotypes and proportions of
offspring.

27. Solve the following problems
using a Punnet Square
 A green plant (Gg) is crossed with yellow (gg)
plant. Determine the possible offspring.
 A red flower (RR) is crossed with white flower
(rr).
 A homozygous tall plant is crossed with
heterozygous tall plant. (short is the recessive
size).

28. Non-Mendelian Inheritance
 Type of inheritance wherein the patterns of
phenotypes does not coincide with those
that was presented in the Mendelian Law of
Inheritance

29. 1. Incomplete Dominance
 A form of intermediate inheritance in
which one allele does not completely
dominate another allele, resulting a new
phenotype.

30. Example
 Red snapdragon and white snapdragon
results is Pink snapdragon.

31. Incomplete Dominance

32. 2. Codominance
 Both alleles are expressed equally in the
phenotype of the heterozygous
 Red and White flower the results is red and
white flower

33. CODOMINANCE

34. Multiple Alleles
 A genes that is controlled by more than two
alleles
 Example : Blood types

35. Blood types
 A , B, AB, O
 Antigen A and B
 Blood type O has no antigen
Blood Type Genotypes
A IA IA, IA i
B IB IB, IB i
AB IA IB
O ii

36. Problem 1.
 A couple gives birth to a baby boy. Both
parents have blood type AB. However
there is a confusion in the hospital. There
are two babies which have unknown
parents. The first baby has blood type B,
while the second baby has blood type O.
Help the couple find their son.

37. Sex Determination
 What determines the sex of
an individual?
 How do sex chromosomes
affect other traits found in
other chromosomes?

38. A karyotype is a visual presentation of the
appearance and number of chromosomes of an
individual.

39. Sex Chromosomes and Sex
Determination
 In each cell, humans have 46 chromosomes
or 23 pairs of chromosomes for both males
and females. Twenty-two (22) pairs are
somatic chromosomes. 23rd pairs consists of
sex chromosomes.
 Male XY non identical
 Female XX identical

40. How is Sex determined and
inherited?
 When an egg is fertilized by a sperm with a
Y chomosomes, the offspring is Male.
 When an egg is fertilized by a sperm
carrying an X chromosomes, the offspring
is Female.

41. How is Sex determined and
inherited?
 What percent of children would
you expect to be Male or
Female?
 50% Female
 50% Male

42. The first 22 pairs of homologous chromosomes are called
autosomes or autosomal chromosomes.
The 23rd pair of chromosomes determines the sex of the
individual and are called sex chromosomes.
The sex chromosomes of a female are XX.
The sex chromosomes of a male are XY.

43. ASSIGNMENT
 DEFINE THE FOLLOWING
CONCEPTS
A. SEX LINKED
B. SEX LIMITED
C. SEX INFLUENCED TRAITS