16. what is polygenic inheritance?
a. give an example.
mutations and recombination
17. what are linked genes?
18. what are sex - linked traits?
a. give an example.
19. in morgan’s fruit fly studies, wing size and body color were linked genes. however, some offspring had phenotypes that did not match the parents. what are these called?
a. what was the mechanism that allowed this recombination to occur?
20. define the three types of chromosomal errors that can occur as a result of crossing over.
a. nondisjunction
b. translocation
c. inversion

Question

Accepted Answer

### Question 16 (Polygene Inheritance)
#### Brief Explanations:
Polygenic inheritance is a pattern where a trait is controlled by multiple genes (polygenes), each with a small effect. These traits show continuous variation (e.g., human height, skin color). For example, human skin color: multiple genes (e.g., 3 - 6 genes) contribute to the amount of melanin, leading to a range from very light to very dark.
#### Answer:
- **Definition**: Polygenic inheritance is the inheritance of a trait controlled by two or more genes (polygenes), where each gene has a small additive effect on the phenotype, resulting in continuous variation (e.g., height, skin color, eye color in humans).
- **Example**: Human skin color. Multiple genes (e.g., 3 - 6 genes) influence the amount of melanin produced. Different combinations of alleles for these genes lead to a spectrum of skin colors from very light to very dark.

### Question 17 (Linked Genes)
#### Brief Explanations:
Linked genes are genes located on the same chromosome and tend to be inherited together because they do not assort independently during meiosis (unless crossing over occurs between them). They violate Mendel’s law of independent assortment for genes on different chromosomes.
#### Answer:
Linked genes are genes that are located on the same chromosome. Because they lie close together on the chromosome, they are usually inherited together as a unit during meiosis, rather than assorting independently (unless separated by crossing over).

### Question 18 (Sex - linked Traits)
#### Brief Explanations:
Sex - linked traits are traits controlled by genes located on the sex chromosomes (X or Y in humans). X - linked traits are more common (since the X chromosome is larger and carries more genes). Males (XY) are more likely to express X - linked recessive traits because they have only one X chromosome.
#### Answer:
- **Definition**: Sex - linked traits are traits whose genes are located on the sex chromosomes (X or Y chromosome). In humans, most sex - linked traits are X - linked (due to the larger size of the X chromosome and more genes it carries).
- **Example**: Hemophilia (X - linked recessive). The gene for blood - clotting factor is on the X chromosome. Males (XY) with a recessive allele on their single X chromosome will have hemophilia, while females (XX) need two recessive alleles (one on each X) to have the disorder. Another example is red - green color blindness (also X - linked recessive).

### Question 19
#### Brief Explanations:
In Morgan’s fruit fly experiments, when linked genes produced offspring with non - parental phenotypes, these offspring are called recombinant offspring. The mechanism for this recombination is crossing over, which occurs during prophase I of meiosis. During crossing over, homologous chromosomes exchange segments of DNA, which can separate linked genes.
#### Answer:
- The offspring with non - parental phenotypes are called **recombinant offspring** (or recombinants).
- a. The mechanism is **crossing over** (or genetic recombination) that occurs during prophase I of meiosis. During this stage, homologous chromosomes pair up (synapsis) and exchange segments of DNA (chromatids), which can break the linkage between genes on the same chromosome, resulting in new combinations of alleles.

### Question 20
#### Brief Explanations:
- **Nondisjunction**: Occurs when homologous chromosomes (in meiosis I) or sister chromatids (in meiosis II) fail to separate properly. This leads to gametes with an abnormal number of chromosomes (aneuploidy), e.g., Down syndrome (trisomy 21) is caused by nondisjunction of chromosome 21.
- **Translocation**: A chromosomal error where a segment of one chromosome breaks off and attaches to a non - homologous chromosome. For example, in chronic myeloid leukemia, a translocation between chromosomes 9 and 22 (the Philadelphia chromosome) occurs.
- **Inversion**: Happens when a segment of a chromosome breaks off, rotates 180 degrees, and reattaches to the original chromosome. This can disrupt gene function or affect crossing over. For example, some forms of hemophilia can be caused by inversions on the X chromosome.
#### Answer:
- a. **Nondisjunction**: The failure of homologous chromosomes (during meiosis I) or sister chromatids (during meiosis II) to separate correctly during cell division. This results in gametes with an abnormal number of chromosomes (e.g., gametes with n + 1 or n - 1 chromosomes, leading to aneuploidy in offspring like trisomy or monosomy).
- b. **Translocation**: A type of chromosomal rearrangement where a segment of one chromosome breaks off and becomes attached to a non - homologous chromosome. This can disrupt gene regulation or cause fusion genes (e.g., the Philadelphia chromosome in leukemia is a translocation between chromosomes 9 and 22).
- c. **Inversion**: A chromosomal aberration where a segment of a chromosome breaks off, rotates 180° (inverts), and then reattaches to the original chromosome. This can alter gene order and may affect crossing over during meiosis, potentially leading to abnormal gametes.

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Question

Explanation:

Question 16 (Polygene Inheritance)

Answer:

Question 17 (Linked Genes)