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Gene Linkage. Inheritance Patterns for ---Two Genes on the Same Chromosome ---Genes on the Sex Chromosomes . Sex Determination. Sex Chromosomes : homologous chromosomes that differ in size and genetic composition between males and females. Sex Determination.

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gene linkage

Gene Linkage

Inheritance Patterns for

---Two Genes on the Same Chromosome

---Genes on the Sex Chromosomes

sex determination
Sex Determination

Sex Chromosomes: homologous chromosomes that differ in size and genetic composition between males and females

sex determination3
Sex Determination

Autosome: any chromosome that is not a sex chromosome

Humans have 22 autosome pairs and 1 pair of sex chromosomes

sex determination4
Sex Determination

Female Male

XX x XY

X X

XX

XX

X

Y

XY

XY

Phenotypic Ratio of Offspring

½ Female + ½ Male

sex linked genes

Xh

Females can be

homozygous or heterozygous for

traits on the

X chromosome

Males are

hemizygous for

traits on the

X chromosome

Dad

XhY

Sex Linked Genes

Hemophilic Male Non-hemophilic

Female

(father is hemophilic)

XhY x XHXh

XH Xh

XHXh

XhXh

Xh

Y

XHY

XhY

Phenotypic Ratio of Offspring

¼ hemophilic males + ¼ non-hemophilic males

¼ hemophilic females + ¼ non-hemophilic females

patterns of inheritance
Patterns of Inheritance
  • Autosomal Dominant
  • Autosomal Recessive
  • Sex-Linked Dominant (X-linked)
  • Sex-Linked Recessive (X-linked)
patterns of inheritance11
Patterns of Inheritance
  • Autosomal Dominant
  • Autosomal Recessive
  • Sex-Linked Dominant (X-linked)
  • Sex-Linked Recessive (X-linked)
  • Mitochondrial Inheritance
how do we study gene linkage
How Do We Study Gene Linkage?

Example from the Fruit Fly

Red eyes, x Pink eyes

Beige body Ebony body

RRBB rrbb

F1: Red eyes, Beige body RrBb

how do we study gene linkage14
How Do We Study Gene Linkage?

Testcross: cross to individual of known genotype

F1: Red eyes X Pink eyes

Beige body Ebony body

RrBb rrbb

how do we study gene linkage16

R B

r b

R B

r b

R B

r b

How Do We Study Gene Linkage?

If genes are linked:

Red eyes, x Pink eyes

Beige body Ebony body

F1: Red eyes, Beige body

how do we study gene linkage17

R B

r b

R B

R b

r b

r B

How Do We Study Gene Linkage?

F1: Red eyes, Beige body

X

Alleles are inCis Configuration

Four types of gametes are produced Parental Recombinant

how do we study gene linkage18

r b

R b

r b

R B

R B

r B

r b

r b

r b

r b

r b

r b

r B

R B

r b

R b

r b

How Do We Study Gene Linkage?

F1:Red eyes X Pink eyes

Beige body Ebony body

genetic map units
Genetic Map Units

1% recombination = 1 map unit

108 + 112 x 100 = 22%

1000

These genes are located 22 map units apart on the same chromosome.

Map is drawn as:

R B

I 22 map units I

how do we study gene linkage21

r B

R b

39%

11%

r B

r b

39%

11%

R b

R B

78%

22%

How Do We Study Gene Linkage?

Knowing the gene distance allows us to predict the expected percentages of each type of gamete.

Alleles are inTrans Configuration

X

Parental Recombinant

gene linkage summary
Gene Linkage Summary
  • Linked genes tend to be inherited together in their original, parental arrangement.

B. Alleles of linked genes can be separated by crossing over (recombination) during meiosis.

  • Distance between genes is calculated as 1% recombination = 1 map unit.
  • Gene distances can be calculated for genes that are less than 50 map units apart. At 50 map units and beyond, we cannot distinguish between genes far apart on the same chromosome and genes on separate chromosomes.