sex linked genes and recombinants, linkage, etc

Question 1

autosomal genes

Answer 1

inherited through recessive alleles or dominant alleles
n=22
non-sex related

Question 2

x-linked genes

Answer 2

recessive and dominant inheritance
n=1

genes found on x-chromosome
(more genes are x-linked)

Question 3

y-linked genes

Answer 3

passed down by male lineage only
genes found on y chromosomes
(less genes are known to be y linked)

Question 4

recessively inherited disorders

Answer 4

only show up in homozygous recessive individuals (aa)

need to get both or 2 copies of the gene to be affected

both affected parents —> affected offspring

Question 5

what does a autosomal recessively inherited disorder look like on pedigree

Answer 5

half filled in squares/circles; equal chance for affected males/females

affected offspring often from unaffected parents

skipping between affected offspring generation could occur

2 heterozygotes = 1/4 probability of child being affected

Question 6

autosomal dominant traits on pedigree

Answer 6

affected children have at least one affected parent

doesn’t skip generations

equal # of affected males and females

unaffected parents dont produce affected children (other than by mutation)

Question 7

autosomal dominant disorders

Answer 7

associated with the dominant allele
affected have Aa or AA genotype

just need one copy of the gene to be affected

Question 8

autosomes vs sex chromosomes

Answer 8

chromosomes 1-22 are autosomes

if an allele of a gene on autosomes specify a trait, you can inherit those alleles from either parent

last pair of chromosomes #23 = sex chromosome

Question 9

z-w chromosomal system

Answer 9

birds snakes butterflies and fish

z=male
z w=female

Question 10

x-o chromosomal system

Answer 10

insects
x = male

xx= females

Question 11

haploid-diploid chromosomal system

Answer 11

bees ants wasps

diploid = female (develop from a fertilized egg)

haploid= male
(develop from an unfertilized egg)

Question 12

which sex chromosome determines sex of a human child

Answer 12

mainly sperm

Question 13

sex linked genes

Answer 13

genes found on one sex-chromosome, but not the other one

Question 14

many ___ cause diseases in humans

Answer 14

x-linked alleles
these diseases occur more frequently in male
^ only need one X to have the gene

Question 15

x-linked recessive pedigree

Answer 15

more affected males than females

all sons of afffected females will be affected

affected daughters have affected fathers

can skip generations

Question 16

x-linked dominant pedigree

Answer 16

affected fathers have 100% affected daughters

Question 17

for an x-linked recessive trait to be expressed what must occur

Answer 17

a person with XX needs two copies of the allele(homozygous)

a person with XY only needs 1 copy of the allele (hemizygous)

Question 18

why are males more likely to have x-linked recessive genes

Answer 18

they only need 1 allele whereas females need two

Question 19

hemophilia A

Answer 19

caused by x-linked recessive genes
dominant allele = X^H
recessive = X^h-A

encodes defective version of a clotting protein

Question 20

x-activation in female mammals

Answer 20

in early embryo, all X chromosomes are initially active and cells have both alleles

one of the two X chromosomes is randomly inactivated in each somatic cell, which becomes the Barr body

Question 21

heterozygous females for a sex-linked trait will have

Answer 21

a mosaic for that character

ex: cat with black and orange fur

Question 22

mendel’s law of independent assortment

Answer 22

separation of homologous chromosomes during metaphase I
explains why he always observed a 9:3:3:1 phenotypic ratio in the F2 generation when he followed 2 characters at a time

Question 23

linkage / linked genes

Answer 23

when two or more genres are close together on the same chromosome, then they tend to be transmitted as a unit

Question 24

linkage groups

Answer 24

group of genes that tend to stay together during meiosis

these genes don’t follow the law of independent assortment

Question 25

genetic recombination

Answer 25

production of offspring with combination of traits that differ from those found in either P generation parent

unlinked genes on the same chromosome can undergo crossing over with other chromosomes to produce new allele combinations

Question 26

nonrecombinatn vs recombinant

Answer 26

nonrecombinant offspring match P generation parents

recombinants have new combinations of alleles/traits that don;t match the parents

Question 27

crossing over with linked vs unlinked genes

Answer 27

unlinked genes on the same chromosome can do more crossing over and increases the likelihood or recombinants

linked genes are less likely to have crossing over lead to new allele combinations

Question 28

how do we explain the occurrence of recombinant when genes are linked

Answer 28

crossing over still does occur but at a much lesser rate

Question 29

how does the distance between two genes impact the likelihood of crossing over?

Answer 29

if genes are very close together, a crossover is unlikely to occur in the region between them

if genes are very far apart, a crossover is more likely to occur in the region between them, leading to more recombinants

Question 30

what allows us to determine the relative distance between linked genes based on the likelihood that a crossover will occur between them

Answer 30

genetic mapping

arrangement of genes along a chromosome (genetic map)

Question 31

map distance

Answer 31

recombinant frequency of test crosses

units of map distance —> mu

Question 32

how to calculate map distance

Answer 32

number of recombinants
———————————. * 100
total number of offspring