Genes and chromosomes
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GENES AND CHROMOSOMES. The Chromosome Theory of Heredity. Traits are determined by pairs of genes (alleles) A pair of genes are located on a pair of chromosomes, one gene for each trait on each chromosome of a pair.

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GENES AND CHROMOSOMES

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Genes and chromosomes

GENES AND CHROMOSOMES


The chromosome theory of heredity

The Chromosome Theory of Heredity

  • Traits are determined by pairs of genes (alleles)

  • A pair of genes are located on a pair of chromosomes, one gene for each trait on each chromosome of a pair.

  • In meiosis, the chromosomes and therefore the genes, segregate independently – one of each pair to a gamete

  • In fertilization, gametes unite resulting in a fertilized egg that has two genes for each trait carried on pairs of chromosomes.


Genes and chromosomes

SEX DETERMINATION AND CHROMOSOMES


Genes and chromosomes

A. XX-XY CONDITIONS

IN DROSOPHILA: 2n= 8

P: (6 + XX) ♀ (6+ XY) ♂

G: ( 3+ X); (3+X)(3+X) (3+Y)

HomogametesHeterogametes

Autosomes

(somatic chr)

meiosis

Gonosomes

(sex chr)

6 + XO ♂

6 + XXY ♀

6 + YO zygote dies


Genes and chromosomes

IN HUMANS: 2n= 46

P: (44 + XX) ♀ (44+ XY) ♂

G: ( 22+ X); (22+X)(22+X) (22+Y)

Homogametes Heterogametes


Genes and chromosomes

44 + XO ♀ (TURNER SYNDROME)

44 + XXY ♂ (KLINEFELTER SYNDROME)

44 + YO ZYGOTE DIES

44 + XXX SUPER FEMALE

44 + XYY POSIBLE SERIAL KILLER*


Genes and chromosomes

(TURNER SYNDROME)


Genes and chromosomes

(KLINEFELTER SYNDROME)


Genes and chromosomes

SUPER FEMALE


Genes and chromosomes

B. ZZ-ZW CONDITION

IN CHICKENS: 2n= 18

P: (16 + ZW) ♀ (16 + ZZ) ♂

G: ( 8+Z); (8+W)(8+Z) (8+Z)

HeterogametesHomogametes


Genes and chromosomes

C. XX-X0 CONDITION

IN GRASSHOPPER: 2n= 24

P: (22 + XX) ♀ (22 + X0) ♂

G: (11+X); (11+X)(11+X); (11+0)

HomogametesHeterogametes


Genes and chromosomes

D. HAPLOID –DIPLOID CONDITION

IN HONEYBEES:

P: (QUEEN) ♀2n= 24 (DRONE) ♂n= 12

G:

meiosis

mitosis

eggs

n

n

n

n

sperm

n

n

fertilization

parthenogenesis

Female larvae (2n)

Differentiaton due to difference in diet

Male larvae (n)

QUEEN

WORKERS

DRONES


Genes and chromosomes

In some species of animals, sex is determined by environmental conditions or by the presence or absence of the opposite sex

Bonellia, If there is more of female individuals in the population, the larva develops into male, which is very small and lives as a parasites in the reproductive system of the female.

In amphibians sex determination is affected by temperature of the environment, and also by hormones.


Genes and chromosomes

In certain annelids, when the number of segments of the organism is small, it is a male. When the number of segments increase, the organism becomes female.


Genes and chromosomes

COLOR BLIND PEDIGREE MAP


Genes and chromosomes

dominant inheritance


Genes and chromosomes

recessive inheritance


Genes and chromosomes

a

b

c

d

e

f

1. Determine if the trait recorded in the pedigree below is dominant or recessive and sex-linked or not. Which of the lettered individuals carry an allele for the trait.


Genes and chromosomes

a

b

c

d

e

2. Determine if the trait recorded in the pedigree below is dominant or recessive. Is it sex-linked or not?


Genes and chromosomes

a

b

c

d

3. Below is a pedigree for four generations of a family, some of whose members exhibit a particular trait. From the information in the pedigree, determine if the trait is dominant or recessive, and sex –linked or not sex-linked. Which of the lettered individuals is a carrier- that is, heterozygous-for the trait?


Genes and chromosomes

a

b

c

d

f

e

4. Determine if the trait recorded in the pedigree below is dominant or recessive and sex-linked or not. Which of the lettered individuals are heterozygous for the trait?


Genes and chromosomes

O

a

O

A

b

B

O

c

f

A

e

B

d

A

B

AB

O

5. The pedigree below shows the blood types of some individuals. List all the possible genotypes of each lettered individuals.


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