Chromosomal and Molecular Basis of Inheritance

Question 1

How many chromosomes do the nuclei of human cells contain (except for gametes)?

Answer 1

• diploid (2n) number 46
• 23 pairs of homologous chromosomes

Question 2

How many chromosomes do human gametes have?

Answer 2

• haploid cells (n) that contain 23 chromosomes

Question 3

What are homologous chromosomes?

Answer 3

• pairs of chromosomes: one from father (sperm) and one from mother (egg)
• look similar and carry genes for the same traits but not necessarily the same expression of traits

Question 4

How many sex chromosomes

Answer 4

• 2 out of 46 chromosomes are sex hormones X and Y which determine genetic sex

Question 5

What are autosomes?

Answer 5

• 44 out of 46 chromosomes
• 22 pairs of autosomes
• guide the expression of other traits

Question 6

What is the human karyotype?

Answer 6

• diploid chromosomal complement displayed in homologous pairs

Question 7

What is the diploid genome?

Answer 7

• genetic (DNA) makeup
• represent 2 sets of genetic expressions: one from egg and one from sperm

Question 8

Difference between gene and genome?

Answer 8

• specific segment of DNA is gene
• genome is entirety of genetic material inside the organism (complete set of DNA)

Question 9

What are alleles?

Answer 9

• matched genes, which are at the same location on homologous chromosomes
• two or more versions of a genetic sequence at a particular region on a chromosome

Question 10

What do alleles do?

Answer 10

• they code for the same or alternative forms of a given trait

Question 11

What does it mean by homozygous and heterozygous?

Answer 11

• homozygous: when 2 alleles controlling a trait are the same (JJ or jj)
• heterozygous: when 2 alleles are different (Jj)

Question 12

Dominant and recessive alleles

Answer 12

• dominant allele: one allele that suppresses the expression of its partner (capital letter)
• recessive allele: one allele that is masked by its partner (small letter)

Question 13

How are dominant alleles expressed?

Answer 13

• when they are present in either single or double does
• JJ or Jj

Question 14

How are recessive alleles expressed?

Answer 14

• when expressed in double dose only
• jj

Question 15

Genotype and phenotype

Answer 15

• genotype is a person’s genetic makeup
• phenotype is the way that genotype is expressed

Question 16

2 important points about meiosis 1 metaphase

Answer 16

(1) two alleles determining each trait are segregated: distributed to different gametes
(2) Alleles on different pairs of homologous chromosomes are distributed independently of each other
- each gamete has a single allele for each trait
- that allele represents only one of 4 possible parental alleles

Question 17

What happens when there are errors in distributions of alleles?

Answer 17

• cancer progression, infertility and Down syndrome