Genetics Flashcards
Give an exemple of a character and a trait that applies.
Character: eye color, skin color, height, etc.
Traits (eye color):blue, green, brown, etc.
traits (skin color): brown, tanned, white, etc.
traits (height): tall, short, average, etc.
What does true-breeding mean?
Individuals that have 2 copies of the same allele, meaning homozygous
What is the name of the original generation?
Parental generation
For the Mendel experiment the parental generation have to be pure. What is another word for pure?
True-breeding
Why does the parental generation need to be true-breeding?
Because we want a first filial generation that completely has both recessive and dominant allele for the experiment to prove useful
What is the name of the generations that come after the parental generation?
(First, second, third, etc.) Filial generation
What is a monohybrid cross?
involves the dominant and recessive trait from the same character crossing together
What is the genotype ratio of the F2 generation in Mendel’s experiment?
3:1
What is the particulate theory?
It is the process in which the discrete particles that are responsible for inheritance (existing in pairs) seperate during gamete formation
What is a gene?
It is Mendel’s unit of inheritance (a characteristic)
What are alleles?
They characterize the gene. An alternative form/a variation of the gene.
Ex.: Gene: the color of the eyes
Allele: blue, brown, green, etc.
What does homozygous mean?
Having two copies of the same allele
What does heterozygous mean?
Combination of two different alleles
What is a genotype?
Composition of the organisms’ alleles for a gene (combination of allele ex.:SS)
What is a phenotype?
The physical appearance of the organism
What is Mendel’s first law? Explain.
The law of segregation: 2 alleles separate when an individual makes gametes
What is the specific location of a gene?
The locus
What is the meiotic interphase?
The homologous chromosomes duplicate
What is meiosis I?
2 chromosomes are separated into 2 daughter cells
What happens in meiosis II?
The 2 daughter cells each divide in two (meaning 4 gametes at the end). Each gamete is haploid
What is Mendel’s second law?
The law of independent assortment: alleles of different genes (ex.: Ss and Yy) assort into gametes independently from each other
How do you calculate the probabilities of the outcome of dihybrid crosses (ex. SSYy)?
Multiply the outcomes from each of the individual monohybrid components. Do a Punnet scare to find the possible allelic combination.
An F1 (dihybrid) cross of SsYy generates
1/4 SS, 1/Ss, 1/4 ss, and 1/4 YY, 1/2 Yy, 1/4 yy.
The probability of the SSYy genotype is the probability of SS genotype (1/4), times the probability of the Yy genotype (1/2), which is 1/8 (1/4 x 1/2 = 1/8)
How is human genetics studied?
By using pedigrees (not very accurate)
What is autosomal dominant inheritance?
It is a pedigree analysis of the dominant allele for a given phenotype that:
- Every affected person has an affected parent
- About half of the offspring of an affected person are also affected (assuming only one parent is affected
- The phenotype occurs equally in both sexes
What is autosomal recessive inheritance?
It is a pedigree analysis of the dominant allele for a given phenotype that:
- If neither parent has a given phenotype, but it shows up in their progeny, the trait is recessive and the parents are heterozygous
-Half of the children from such a cross will be carriers (heterozygous for the trait) - The chance of any one child’s getting the trait is 1/4
What is the most common type of allele in a population?
The wild type (seen more often than mutant allele)
What is incomplete dominance?
When heterozygotes show intermediate phenotype, which might seem to support the blending theory
Ex.:
RR (red) and rr (white) are the parents
F1: are all pink (Rr) because the red (RR), the dominant allele is incompletely dominant
When the F1 generation interbreeds
F2: 1/2 pink, 1/4 red, 1/4 white
What is codominance?
When 2 different alleles for a gene are both expressed in the heterozygotes
Ex.: In the human ABO blood group system the alleles for blood types are A, B, and O.
- AA or AO, results in type A.
- BB or BO, results in type B.
- OO results in type O.
- AB results in type AB. The alleles are called codominant.
What is pleiotropy?
Single alleles that have more than one distinguishable phenotypic effect
Pleiotropy is caused by different proteins produced by the same allele. True or False. Explain.
False, it is caused by the same proteins produced by the same allele
What is episatsis?
When the alleles of one gene cover up or alter the expression of alleles of another gene
What are complementary genes?
It is another form of epistasis in which two genes are mutually dependent; the expression of each depends on the alleles of the other.
What is polygenic inheritance/quantitative trait loci?
A group of several genes that control complex inherited characteristics. Since there is constent variations in these characteristics.
What usual factors cause variations in alleles?
- Multiple genes with multiple alleles (polygenes)
- Environmental influences on the expression of the genes
What is a factor that increases or decreases the likelihood of recombination? Explain how that factor affects recombination.
The distance between the genes affect recombination.
- Genes close to each other, usually stay together
- Genes that are far from each other, more likely to separate during recombination
What is recombinant frequency?
It’s the frequency that measures how often 2 genes are separated by crossing over during meiosis
What is chiasma?
The physical space in which the cross-over happens
What are genetic maps for?
Show the arrangement of genes along the chromosome
How genetic maps ususally made?
By using recombination frequency which help to find the distance between genes on a same chromosome.
What are the units of the distances between genes?
Map units
1 mu= centimorgan (cM)= 1%=0.01
How is the map distance between 2 genes calculated?
Separate the parental types from the recombinants type
Find the recombinant frequency
Recombinant frequency = (nb. recombinant type A +nb. recombinant type B)/nb. total of individuals in the progeny
Then find the map distance
map distance= 100 x recombinant frequency
What determines the sex of an offspring?
The sperm
What is Turner Syndrome and its effect?
It is a syndrome characterised by the XO condition. It results in females who are physically abnormal but mentally normal and usually sterile.
What is Klinefelter syndrome and its effects?
Is characterized by an XXY condition and results in males who are taller than average and always sterile
What is SRY and what happens if it’s missing? What does it do?
The maleness-determining gene and if it’s missing the individual will be phenotypically a female.
SRY (sex determining region) gene codes for a functional protein. If this protein is present, testes develop.
What is DAX1?
It is a gene on the X chromosome that produces anti-testis factor
What is hemizygous and who are hemizygous?
It is when an individual has only one copy of a gene
All males are.
Why are males hemizygous?
Y chromosomes carry very few genes. It doesn’t have all the genes in the X chromosome
What are carriers?
Carry the X chromosome with a mutation but does not have it
What is X-linked recessive?
A pedigree analysis show that:
-The phenotype appears much more often in males than in females
-A male with the mutation can pass it only to his daughters
- Daughters who receive one mutant X are heterozygous carriers
-The mutant phenotype can skip a generation if mutation is passed from male to his daughter and then to her son
What is an X-linked dominant phenotype?
A pedigree analysis shows that:
- The trait is never passed from father to son
- All the daughters of an affected male and a normal female are affected
- Matings of affected females and normal males produce 1/2 the sons affected and 1/2 the daughters are affected
What is mitochondrial (maternal) inheritance?
Only passed down by the mother since the egg is the only gamete that can contain cytoplasm and organelles
A pedigree analysis shows that:
- An affected mother passes the trait to all her children
- An affected father passes the trait to none of the children
