Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Genetics > Sex linkage > Flashcards

Sex linkage Flashcards

You may prefer our related Brainscape-certified flashcards:
Biology 101 flashcards
1
Q

chromosomes

A

A structure composed of DNA and associated proteins that in total contain the genome of an organism.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Autosomes

A

equally represented in both sexes and are the majority of our chromosomes – 22 of our chromosomes are autosomes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Sex chromosomes:

A

differently represented in the sexes (last chromosomes, 23 is sex chromosome)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

homogametic

A

the sex of a species in which the sex chromosomes are identical
Females
XX in mammals and some insects such as Drosophila

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

heterogametic

A

Males

XY in mammals and some insects

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Thomas Hunt Morgan

A

helped support this finding in his studies in Drosophila melanogaster (Common fruit fly) ~1910’s

Flies were captured from the environment and phenotypes observed under a microscope

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Wildtype

A

phenotype that is most common in a population, denoted with “+”(usually corresponding to dominant trait, talking about most common not whether its dominant or recessive)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Mutants

A

phenotype different from wildtype, commonly denoted with “m” - not always recessive

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Carriers

A

carries both the dominant and recessive alleles for a trait (ie heterozygous)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Why did Morgan use flies?

A

Easy to study due to short life cycles (12-14 days)

Could raise 100s of generations in short amount of time

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Autosomal inheritance

A

Hereditary transmission of genes carried on autosomes.
not sex linked

means that males and females are equally likely to inherit the gene

Mendel looked at autosomal inheritance

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Sex-linked inheritance

A

i

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

X-linked inheritance

A

inheritance of genes on the X chromosome

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What are the indicators of Sex-linked inheritance

A

Males and females have different phenotypic ratios in the F1 and F2

Reciprocal crosses give different results

Female wildtype x male mutant ≠ female mutant x male wildtype

“Criss-cross” inheritance

Eg a recessive trait is passed from recessive father to carrier daughter to recessive grandson

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

“Criss-cross” inheritance

A

Eg a recessive trait is passed from recessive father to carrier daughter to recessive grandson

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What did Morgan first do with the flies?

A

Did a single mendilian cross for eye color

Morgan’s wife found a mutant male fly with white eyes

Wildtype is brick red eyes

Mutant white-eyed male was crossed with wild-type red-eyed female

1273 F1 flies, all red eyes

Suggests red is dominant over white

F1’s were then crossed to produce F2 generation
2459 red-eyed females

1011 red-eyes males

782 white-eyed males

Morgan had expected a 3:1 ratio of red eyes to

NOTE: No white-eyed females!

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What was the second cross that Morgan do and what did it suggest?

A

When Morgan performed a reciprocal cross of his first cross (ie red-eyed male with a white eyed female), it resulted int:

Red-eyed females in F1

White-eyed males in F1

The F2 showed equal proportions of red-eyed and white-eyed males and females

The results of this cross were completely different from the first cross he did (previous slide)

Confirmed eye-color was inherited differently from other traits

Inherited differently in sexes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Hemizygous

A

have only one x chromosome so whatever allele is present on that x chromosome that’s what trait they will express

Need only 1 copy of the allele for the phenotype to be expressed

Inherited from the mother

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Do sex linked traits follow mendel rules

A

Yes if we look at the traits as a whole excluding the sex

ex- morgans flies in F2 just looking at eye colour have 3:1 ratio

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What did morgan’s first cross using sex chromosomes show?

A

Single X chromosome in the male carries a recessive allele w
X^w
Females carry 2 X chromosomes, each carrying an allele for eye colour
X^w+ X^w+
In the F2, we see that males are 50% red eye and 50% white eye

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What did Morgans reciprocal cross using sex chromosomes using sex chromsomes show?

A

now supports Morgan’s idea of X-linked inheritance

The results in the F1 and F2 from this cross and the one on the previous slide are different

If you need to, go back to Mendel’s peas and look at the results of reciprocal crosses there

Notice there that the results are the same in the F1 and F2

Note in this reciprocal cross, we get a phenotypic ratio in the F2 as 1:1 red to white

22
Q

Why were some of the results the flies produced in the reciprocal cross were they expected why did this occur?

A

Some of the flies did produce unexpected results in the reciprocal cross

White-eyed females

Red-eye males

Occurred ~1 in every 2000 F1 flies

Due to nondisjunction (failed chromosome separation)

Produces viable XXY(females in flies) and X0(males in flies)(0 means missing a chromosome) flies

XXX and YO flies are lethal

23
Q

X-linked recessive

A

transmission of recessive allele on the X chromosome

24
Q

X-linked dominant

A

transmission of the dominant alleles on the X chromosome

25
Q

Autosomal recessive

A

transmission of recessive alleles on autosomes (ie aa)

26
Q

Autosome dominant

A

transmission of dominant alleles on autosomes (ie AA, Aa)

Autosomal inheritance follows the typical Mendelian genetics patterns we’ve been discussing thus far

27
Q

What are some examples of X-linked recessive transmission in humans?

A

Colour-blindness (OMIM 303800)

Hemophilia A (OMIM 306700)

Muscular dystrophy (OMIM 310200 (Duchenne type), OMIM 300376 (Becker type))

Phenotype is expressed in homozygous recessive females (X^aX^a) and hemizygous males (X^aY)

Same pattern as the white-eyes in Drosophila

28
Q

If we had wildtype mother (X+X+ ) and hemizygous affected father (X^cbY)

A

All daughters will be carriers (X+Xcb)

All sons would be wildtype (X+Y)

29
Q

If we had a carrier mother (X+Xcb) and wildtype father (X+Y)

A

Half of the daughters will be carriers (X+Xcb) and half wildtype (X+X+)

Half of the sons will be affected (XcbY) and half wildtype (X+Y)

30
Q

Can we have a colour-blind female? How?

A

Father in colour blind mother is a carrier

31
Q

What are some examples of X-linked Dominant transmission in humans?

A

Rett syndrome (OMIM 312750)- only affects females

Amelogenesis imperfecta (abnormal tooth enamel development, OMIM 301200)

Phenotypes expressed in homozygous dominant females (XDXD) and hemizygous males (XDY)

32
Q

What are some things to note in X-linked Inheritance?

A
  1. Recessive and dominant refer to X-linked inheritance in females

Males are hemizygous so will also express the trait based on what is present on the X-chromosome

  1. Probability of transmission of X-linked traits to offspring is not the same for each sex

 Females follow typical patterns seen in autosomal inheritance

 Males always transmit their X chromosome to female offspring and Y to male offspring

  1. Females get one X chromosome each from Mom and Dad while males get their X chromosome (and therefore X-linked alleles) from Mom and Y chromosome from Dad

Y-linked genes are solely within male lineages (patrilineal)

Generally linked to male fertility and development and other male-specific traits

33
Q

y- linked transmission

A

Occur on the Y chromosome

Smaller chromosome compared to X chromosome

Fewer genes (<50), not involved in sex determination

Females never carry Y chromosomes, so traits are solely male

Traits are “holandric”, or wholly male

Recessive and dominance not applicable

34
Q

What is an example of a y linked trait?

A 
Hairy ears (HE)
we had a wildtype mother (X+X+) and affected male (X+Y HE)

Daughters will all be wildtype (not hairy ears, X+X+)

Sons will all have hairy ears (X+Y HE), ie all affected

35
Q

complete penetrance

A

Most geneticists assume that the variation we see in phenotypes is due to differences in genotypes

Only valid if the genotype always produces the same phenotype

Mendels peas

36
Q

Sex-limited traits

A

Alleles are carried in both sexes, but the phenotype only shows up in one sex
Behave like autosomal traits but only in one sex

Ex. Breast development and ability to produce milk in female mammals

FYI -> Males can get breast cancer too (but less than 1% of all breast cancers)! They just don’t have developed breast tissues

37
Q

Sex-influenced traits

A

Inheritance patterns vary between the sexes even if genotype is the same

Usually influenced by hormone levels

Often autosomal

38
Q

What are some examples of sex-limited traits

A

Breast and milk production in female mammals

Horn development in male sheep, cows, and other hoofed animals

Certain behaviors in sexually dimorphic animals

Eg courtship behaviors in cranes differ between males and females

Eg male canaries sing different songs as a result in increased male hormones at certain times of the year

39
Q

What is an example of sex influenced traits?

A

chin beards in goats

Bearding is inherited as an autosomal trait determined by two alleles, B1 and B2

Homozygous states in both sexes are the same:  B1B1 = beardless (recessive)

B2B2 = bearded (dominant)

The heterozygote state varies among the sexes though

Males B1B2 = bearded

Females B1B2 = beardless

Overall, a 3:1 ratio present for the trait for each sex

Another common example in humans: male patterned baldness

40
Q

Sex determination

A

Encompasses the genetic and biological processes that produce male and female characteristics in a species

41
Q

Chromosomal sex

A

the presence of sex chromosomes associated with male and female in a species

Determined at fertilisation based on contribution from parental gamete

42
Q

Phenotypic sex

A

the internal and external morphology found in each sex

Determined by gene expression and development of sexual characteristics

43
Q

Aneuploidy

A

In humans, the X and Y chromosomes are homologues

Small region in the Y chromosome acts as a homologue to the X chromosome

Results in sperm with either 1X or 1Y

44
Q

What happens in Drosophila, nondisjunction?

A

, nondisjunction in meiosis 1 within females results in:

1 gamete with no X chromosomes (0)

1 gamete with extra X chromosome (XX)

When mated with a normal male gamete, can result in 

XXX (lethal), XXY (non -lethal) females

X0 (non -lethal), YO (lethal) males

45
Q

How is sex determined in Drosophilia?

A

The number of X chromosomes in relation to the number of haploid autosomal chromosomes determines sex
X:A or X:autosome ratio

XY, XYY, X0 = males, Y0 males are never observed (lethal)

XX, XXY = females, XXX females rarely observed (lethal)

46
Q

How is sex determined in mammals?

A

Mammals also have 2 sex chromosomes: X and Y  Sex determination depends on the presence of the Y
chromosome
 Y chromosome has a SRY (sex determining region on
Y) gene that is expressed  Males = XY, XXY, XYY
 Females = XX, X0, XXX

47
Q

What does the expression of the SRY do?

A

also elicits a cascade of events that lead to the development of male internal and external structures
 As embryos, we contain undifferentiated gonadal tissues
 Wolffian ducts will develop into male sexual and
reproductive structures
 In males SRY expression initiates development
 Müllerian ducts will develop into female sexual and reproductive structures
 In females, the absence of SRY allows development

48
Q

How is sex determined in birds, some reptiles, certain fish, moths,
butterflies?

A

Z/W system
 Females = ZW (heterogametic and
hemizygous)
 Males = ZZ (homogametic)
 Reciprocal crosses exhibit different results compared to normal Mendelian reciprocal crosses
 Z-linked genes behave like X-linked genes in mammals
 W-linked genes are matrilineal (only occurs in females)

49
Q

How is sex determined in Roundworms, C. elegans, nematodes

A

X:A ratio determines sex
 XX = hermaphrodite, usually self-fertilises
 Occasional nondisjunction results in X0(male) individuals
These individuals act as males producing “super-sperm” that can outcompete
the sperm from hermaphrodites Increases genetic variation!
When the mate with an XX, offspring are 1XX: 1X0 (hermaphrodite: males)

50
Q

How is sex determined in monotremes?

A

Multiple sets of sex chromosomes can be involved

 Monotremes (echidnas and platypus)-> 5 pairs of sex chromosomes!

51
Q

What other ways can sex be determined?

A

environmental factors
Temperature determines sex in sea turtles (<28C = males, >32C = females, 28-32C =
both males and females)
 Some fish change sex throughout their life depending on the temperature of the water! Ex. Clown fish……yes, like in Finding Nemo

52
Q

How is sex determined in plants

A

90% of species are bisexual (“hermaphroditic”) Remaining 10% of species may have
 Separate male and female plants
 Hermaphrodites and males
 Hermaphrodites and females (“inconstant males”)

Genetics (12 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions