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Genetics Key Concepts
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Genetics Key Concepts
Genetics Key Concepts
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1
Question
What is a karyotype and how are chromosomes arranged in it?
Answer
A karyotype is a micrograph in which pairs of homologous chromosomes are arranged in decreasing size. Images are taken of chromosomes stained during metaphase, arranged by size to produce the micrograph.
2
Question
What information can a human karyotype provide?
Answer
A human karyotype shows chromosomes arranged in pairs based on size and shape, including the sex chromosomes. It reveals banded structures indicating DNA density regions and is used to identify chromosomal abnormalities and genetic disorders.
3
Question
What are telomeres and what roles do they play in chromosomes?
Answer
Telomeres are protective caps on chromosomes made of DNA associated with proteins. They serve to protect the chromosome structure, and recent evidence suggests they might be involved in aging and cancer processes.
4
Question
Define nondisjunction and when it can occur during cell division.
Answer
Nondisjunction is the failure of sister chromatids to properly separate during cell division, occurring during meiosis I or II. This results in gametes with abnormal numbers of chromosomes.
5
Question
What are the consequences of nondisjunction during meiosis for the offspring?
Answer
When gametes with abnormal chromosome numbers from nondisjunction combine during fertilization, the resulting offspring may have an incorrect number of chromosomes, leading to genetic disorders such as Down syndrome.
6
Question
What is Down syndrome and how is it related to nondisjunction?
Answer
Down syndrome is a human chromosomal disorder caused by trisomy 21, where three copies of chromosome 21 are present due to nondisjunction. Its frequency increases with maternal age.
7
Question
Describe what is observed in a karyotype of an individual with Down syndrome.
Answer
The karyotype shows 23 pairs of chromosomes with an extra copy of chromosome 21 (trisomy 21), clearly visible and often circled. The chromosomes are numbered 1 to 22, plus the sex chromosomes.
8
Question
Can nondisjunction affect sex chromosomes as well as autosomes?
Answer
Yes, nondisjunction can occur in both autosomes and sex chromosomes, potentially leading to disorders involving sex chromosome abnormalities.
9
Question
Explain incomplete dominance using the example of flower color.
Answer
Incomplete dominance occurs when the heterozygous phenotype is intermediate between the two homozygous phenotypes. For example, crossing a red flower (RR) with a white flower (rr) produces pink flowers (Rr); self-fertilizing pink flowers produces offspring with a phenotype ratio of 1 red : 2 pink : 1 white.
10
Question
How does the phenotype ratio 1:2:1 in incomplete dominance correspond to the genotypes?
Answer
In incomplete dominance, the 1:2:1 phenotype ratio corresponds to 1 homozygous dominant (RR), 2 heterozygous (Rr), and 1 homozygous recessive (rr) individuals, exhibiting red, pink, and white flowers respectively.
11
Question
What is codominance and how does it differ from incomplete dominance?
Answer
Codominance is a genetic situation where both alleles in a heterozygous individual are fully expressed, unlike incomplete dominance where the heterozygote shows an intermediate phenotype. In codominance, both traits appear simultaneously.
12
Question
What causes red blood cells to change shape in sickle-cell disease?
Answer
Changes in hemoglobin cause red blood cells to change to a sickle shape.
13
Question
What is the characteristic of individuals heterozygous for the sickle-cell trait?
Answer
They have both normal and sickle-shaped red blood cells.
14
Question
What are the three forms of alleles in the ABO blood group system?
Answer
The alleles are I^A, I^B, and i.
15
Question
How do the alleles I^A and I^B interact in the ABO blood group inheritance?
Answer
I^A and I^B alleles show codominance, resulting in blood type AB when both are present.
16
Question
What blood type results from the genotype ii in ABO blood groups?
Answer
Blood type O results from the genotype ii.
17
Question
What does it mean when an inheritance pattern involves multiple alleles?
Answer
It means more than two alternative forms (alleles) of a gene exist in the population, but each individual still carries only two alleles.
18
Question
What is the hierarchy of dominance among the four alleles controlling rabbit coat color?
Answer
The alleles are C, c^ch, c^h, and c, which demonstrate a hierarchy of dominance influencing coat color.
19
Question
What is epistasis in genetics?
Answer
Epistasis is when one allele hides or masks the effects of another allele, affecting the phenotype.
20
Question
How does epistasis affect Labrador retriever coat color?
Answer
Certain alleles (like 'e') can prevent dark pigment from being present in the fur, hiding the effects of other coat color alleles.
21
Question
In Labrador retrievers, what coat color results from the genotype eebb?
Answer
A light yellow coat color with no dark pigment present in the fur.
22
Question
What chromosomes determine an individual's gender?
Answer
Sex chromosomes determine gender, typically the X and Y chromosomes.
23
Question
Explain the outcomes of sex determination using the XY chromosome system.
Answer
An egg (X) fertilized by a sperm carrying X results in XX (female), and fertilization by a sperm carrying Y results in XY (male). The probability of each is roughly 50%.
24
Question
What is dosage compensation and why is it important?
Answer
Dosage compensation balances the expression of genes on the X chromosome between males (XY) and females (XX) to ensure that gene expression levels are similar despite the difference in X chromosome number.
25
Question
What is a Barr body?
Answer
A Barr body is an inactivated X chromosome in female cells, helping achieve dosage compensation.
26
Question
What are sex-linked traits?
Answer
Traits caused by genes located on the X chromosome.
27
Question
Give two examples of sex-linked traits.
Answer
Red-green color blindness and hemophilia.
28
Question
What are polygenic traits?
Answer
Traits controlled by the interaction of multiple pairs of genes, resulting in continuous variation in the phenotype.
29
Question
How does polygenic inheritance affect skin color?
Answer
Skin color results from multiple genes each adding to the amount of pigment, and the combined effects form a range or gradient of pigmentation.
30
Question
How does the number of dominant alleles influence polygenic traits like skin color?
Answer
Having more dominant alleles typically leads to a stronger expression of the trait, for example, darker skin color.