unit 5: heredity

Question 1

how many chromosomes are in a cell?

Answer 1

chromosomes are made up of protein and a single molecule of DNA which is passed from parent to offspring.
there are 23 pairs of chromosomes in human cells.

Question 2

how does a somatic cell compare to a gamete?

Answer 2

somatic cells have 46 chromosomes while gametes are haploid cells with 23

Question 3

sex chromosome vs autosome

Answer 3

sex chromosomes determine the sex of an individual. an autosome is a chromosome not involved in determining sex

Question 4

karyotypes

Answer 4

A karyotype is a display of the chromosome pairs of a cell arranged by size and shape. Karyotypes are prepared from isolated somatic cells which are treated with a drug to stimulate mitosis and then they are grown in culture for several days. Cells arrested when chromosomes are most condensed (metaphase) are stained and then viewed with a microscope. Karyotypes help determine the size of the chromosome, position of the centromere and pattern of stained bands to help identify specific chromosomes.

Question 5

homologous chromosomes

Answer 5

a pair of chromosomes of the same length, centromere position, and staining pattern that possesses the genes for the same characters at the corresponding loci. one is inherited from the mother and one from the father

Question 6

where are gametes produced?

Answer 6

in the gonads (germ cells): testes and ovaries // anther and ovule

Question 7

meiosis

Answer 7

Gametes are produced through meiosis: a type of cell division sexually reproducing organisms with two rounds of cell division but only one round of DNA replication. It produces gametes and enhances genetic variability.

Question 8

what are alleles?

Answer 8

any of the alternative versions of a gene that may produce distinguishable phenotypic effects.
ex) freckles, hair color

Question 9

what is synapsis?

Answer 9

the pairing and physical connection of duplicated homologous chromosomes

Question 10

what is crossing over?

Answer 10

crossing over produces recombinant chromosomes (individual chromosomes that carry genes from two different parents)
an average of one to three crossover events occurs per chromosome pair, depending on the size of the chromosomes and the position of their centromeres

Question 11

when do crossing over and synapsis occur?

Answer 11

Prophase I

Question 12

explain the difference between a monohybrid and dihybrid cross?

Answer 12

cross between two organisms that are heterozygous for the character being followed (or the self-pollination of a heterozygous plant).

A cross between two organisms that are each heterozygous for both of the characters being followed (or the self-pollination of a plant that is heterozygous for both characters)

Question 13

Law of Independent Assortment

Answer 13

cross between two organisms that are heterozygous for the character being followed (or the self-pollination of a heterozygous plant).

Question 14

Incomplete dominance

Answer 14

ncomplete dominance: neither allele is completely dominant, offspring have a phenotype between the parents (red and white flowers having a pink offspring)

Question 15

complete dominance

Answer 15

Complete dominance: phenotypes of the heterozygotes and the dominant homozygotes are indistinguishable (red is dominant over white and produces red offspring)

Question 16

pleiotrophy

Answer 16

Most genes have pleiotrophy (i.e. multiple phenotypic effects). In humans, pleiotropic alleles are responsible for the multiple symptoms associated with certain hereditary diseases, such as cystic fibrosis and sickle-cell disease. Cystic fibrosis affects the cells responsible for producing mucus, sweat, and digestive juices (one gene influencing two or more seemingly unrelated phenotypic traits). Similarly, sickle cell is a pleiotropic disease because the expression of a single mutated HBB gene produces numerous consequences throughout the body.

Question 17

epistasis

Answer 17

a type of gene interaction in which the phenotypic expression of one gene alters that of another independently inherited gene

Question 18

cystic fibrosis

Answer 18

recessively inherited, defective membrane protein for chloride, mucus builds up in lungs, pancreas, digestive tract, poor absorption of nutrients, chronic bronchitis, infections, premature death

Question 19

sickle-cell disease

Answer 19

recessively inherited; low oxygen content leads to deformed red blood cells; clumping and clogging of cells, physical weakness, pain, organ damage even paralysis and brain damage.

Question 20

achondroplasia

Answer 20

dominantly inherited, heterozygotes, have dwarf phenotype, bone defects, 99.99% of population have homozygous recessive genotype

Question 21

huntington’s disease

Answer 21

dominantly inherited, degenerative disease of nervous system, movement and psychiatric

Question 22

chromosome theory of inheritance

Answer 22

genes have specific loci along chromosomes, and these chromosomes undergo segregation and independent assortment

Question 23

law of segregation

Answer 23

when an organism makes gametes, each gamete receives just one gene per copy which is selected randomly

Question 24

why is the fruit fly an excellent subject for genetic studies?

Answer 24

a) single mating will produce hundreds of offspring

b) a new generation can be bred every two weeks

c) the fruit fly has only four pairs of chromosomes, which are easily distinguishable with a light microscope

Question 25

SRY gene

Answer 25

SRY refers to the Sex determining Region of Y, a gene found on the Y chromosome that is required for the development of testes

Question 26

sex-linked gene

Answer 26

A gene located on either sex chromosome. Most sex-linked genes are on the X chromosome and show distinctive patterns of inheritance; there are very few genes on the Y chromosome

Question 27

What is a Barr body?

Answer 27

A dense object lying along the inside of the nuclear envelope in cells of female mammals, representing a highly condensed inactivated X chromosome. Female mammals, including humans, inherit two x chromosomes- twice the number inherited by males; females show a Barr body in their cells to that the cells of females and males have the same effective dose (one copy) of most x-linked genes

Question 28

How is the X chromosome inactivated?

Answer 28

The selection of which X chromosome will form the Barr body occurs randomly and independently in each embryonic cell present at the time of X inactivation. Females consist of a mosaic of two types of cells; those with the active X derived from the father and those with the active X derived from the mother. After an x chromosome is inactivated in a particular cell, all mitotic descendants of that cell have the same inactive X.

Question 29

nondisjunction

Answer 29

an error in meiosis or mitosis in which members of a pair of homologous chromosomes or a pair of sister chromatids fail to separate properly from each other

Question 30

aneuploidy

Answer 30

a chromosomal aberration in which one of more chromosomes are presnet in extra copies or are deficient in number (Ex Trisomy 21)

Question 31

monosomy

Answer 31

refers to a diploid cell that has only one copy of a particular chromosome instead of the normal two. Turner syndrome is a human monosomy, the female has only one X chromosome

Question 32

trisomy

Answer 32

trisomy - refers to a diploid cell that has three copies of a particular chromosome instead of the normal two. Trisomy is trisomic for chromosome 2

Question 33

polyploidy

Answer 33

a chromosomal alteration in which the organism possesses more than two complete chromosome sets. It is the result of an accident of cell division.