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Gamete formation
Meiosis
What are the two parts of sexual reproduction?
Meiosis
Fertilization
Small gametes
Male
Large gametes
Female
What process causes the genetic variation seen in offspring produced by sexual reproduction?
Meiosis
both sexes in the same organism
Hermaphroditism
both male and female reproductive structures in the same organism
Monoecious
either male or female reproductive structures in one organism
Dioecious
What are the sex determining systems?
Chromosomal
Genetic
Environmental
determine the sex of an organism; differ in males and females; X and Y in humans
Sex chromosomes
Chromosomes that are the same in males and females
Autosomes
What are the Chromosomal Sex Determining Systems?
XX-XO
XX-XY
ZW-ZZ
Haplodiploidy
First studied in grasshoppers
XX-XO Sex-Determination
Explain meiosis in XX-XO sex determination
Female: all eggs get one X chromosome
Males: half the sperm get an X chromosome, the other half gets no sex chromosome
sex that produces one type of gametes
Homogametic
sex that produces two types of gametes
Heterogametic
Males and females have the same number of chromosomes
XX-XY Sex-Determination
regions on the X and Y chromosomes allow for pairing during meiosis
Pseudoautosomal
Birds, snakes, butterflies, some amphibians, and fishes
ZZ-ZW Sex-Determination
ZZ
Male
ZW
Female
Bees, wasps, and ants
Haplodiploidy
Haplodiploidy Haploid set
Male
Haplodiploidy Diploid set
Female
No sex chromosomes, only the sex-determining genes; Found in some plants, fungi, protozoans, and fish
Genic Sex-Determining System
Environmental factors like limpet’s position in the stack and temperature in turtles and alligators
Environmental Sex Determination
Turtles: warm temps (>300C)->
Females
Alligators: warm temps ->
Males
The balance (or ratio) of X:A determines
Sex
The X:A stands for
The number of X-chromosomes/the number of haploid sets of autosomal chromosomes
= 1
Female
= 0.5
Male
>1
Metafemale
0.5-1
Intersex
<0.5
Metamale
The importance of the X and Y-chromosomes is demonstrated by the phenotypes that result from abnormal numbers of sex chromosomes:
Turner Syndrome
Klinefelter Syndrome
Jacob’s Syndrome
Poly-X females
Females with a single X chromosome; 1 in 3000 births
Turner Syndrome
One Y-chromosome and multiple X-chromosomes (XXY is most common)
Klinefelter Syndrome
Two Y-chromosomes and an X-chromosome
Jacob’s Syndrome
Triplo-X syndrome (XXX) most common
Poly-X Females
At least one __ chromosome is needed for human development.
X
The presence of a __ chromosome results in development of the male phenotype.
Y
The absence of a __ chromosome leads to female development
Y
The male determining gene(s) must be located on the __ chromosome.
Y
Extra copies of the __ chromosome often leads to developmental problems in both males and females resulting in physical and mental health problems that increase as the number of __ chromosomes increases.
X
sex determining region on Y
SRY-gene
production > male development
Testosterone
substance > degeneration of female reproductive ducts
Mullerian-inhibiting
An XY individual who appears female, but has an intact SRY gene, may have
Androgen Insensitivity Syndrome
Possessing a single allele at a locus
Hemizygous
Phenotypes determined by genes found on the sex chromosomes
Sex-Linked Characteristics
Hemophilia (reduced blood clotting) is an X-linked recessive disease in humans. A woman with hemophilia mates with a man who exhibits normal blood clotting.
What is the probability that their child will have hemophilia?
1/2
equalizes the amount of expression from X-chromosomes in males and females
Dosage Compensation
The inactive X-chromosome
Barr-body
states that the Barr body is the inactive X-chromosome and that X-inactivation is random so that either X chromosome in any given cell can become the Barr body
Lyon Hypothesis
How is the X-chromosome inactivated?
Xist gene
2/3 of the Y chromosome is
Heterochromatin
How many genes does the Y chromosome encode?
50-60
What is a palindrome?
Sequence that reads the same backwards as forward
one allele completely dominant over another allele
Complete dominance
a heterozygous individual has a phenotype that is intermediate between the two homozygous
Incomplete Dominance
both alleles are expressed in a heterozygous individual
Codominance
I^A and I^B are
Codominant
the percentage of individuals having a particular genotype that express the expected phenotype
Penetrance
when a gene is not always expresses so that the phenotype does not match the genotype in every individual
Incomplete penetrance
the degree to which a trait is expressed
Expressivity
(extra digits) can be inherited as a dominant trait, but it is not always expressed
Polydactyly
causes death at an early stage of development, so some genotypes may not appear among the progeny; Affects the Mendelian genotypic and phenotypic ratios in progeny.
Lethal Alleles
ABO blood types in humans are ____, but they also have ____
codominant; complete dominance
Effects of genes at one locus depend on the presence of genes at other loci.
Gene interaction
How does gene interaction differ from dominance?
Gene interaction is interaction between genes at different loci.
Dominance is interaction between alleles at a single locus.
one gene hides (masks) the expression of another gene located at a different locus
Epistasis
the gene that masks
Epistatic gene
the gene that is being masked
Hypostatic gene
Types of Epistasis:
Recessive
Dominant
Duplicate recessive
Recessive Epistasis Ratio
9:3:4
Dominant Epistasis Ratio
12:3:1
Duplicate Recessive Epistasis Ratio
9:7
Turtles and alligators rely on this sex determining system
Environmental Sex Determination
In this sex determining system one or multiple genes dictates the sex of the organism. Common in plants.
Genie Sex Determination
Humans, bees and grasshoppers have this type of sex determination.
Chromosomal Sex Determination
A female grasshopper has the same number of chromosomes as a male grasshopper. True or False
False
In birds, females are the heterogametic sex. True or False
True
Male bees produce gametes by meiotic cell division. True or False
False
In cold temperatures alligator embryos develop as males. True or False
False
A fruitfly with one X chromosome, no Y chromosome and the normal sets of autosomes (2n) will develop as a:
Male
What is the result if the SRY gene on the Y chromosome fails to activate at 6 weeks of development?
The fetus will develop as a female
Bob, who is colorblind, has a child with Sarah, who's father was colorblind. What is the probability that their child with be a boy with colorblindness?
1/4
Sex linked characteristics are
Encoded on a sex chromosome
X-linked alleles are passed from the father to
all his daughters
Who was the fist person to study sex-linked genes in Drosophila?
Thomas Hunt Morgan
A women, who has red-green colorblindness has four sons. What is the probability that all the sons also have red-green colorblindness? Assume normal gamete formation in both the mother and the father.
1
The Xist gene is actively transcribed on the
inactive X-chromosome
What sex-determination system do fruit flies (Drosophila) have?
Genic balance system
The phenotype of the heterozygote is intermediate between the phenotypes of the two homozygotes
Incomplete Dominance
The phenotype of the heterozygote includes the phenotypes of both homozygotes
Codominance
The phenotype of the heterozygotes is the same as the phenotype of one of the homozygotes
Complete Dominance
In epistasis, the _____________gene masks the expression of the ___________________ gene.
Epistatic;hypostatic
Coat color in Labrador Retrievers is determined by two genes exhibiting
Recessive epistasis
Polydactyly is the condition of having extra fingers or toes. Some polydactylous persons possess extra fingers or toes that are fully functional, whereas others possess only a small tag of extra skin. This is an example of
Variable expressivity