Chapter 2: SINGLE-GENE INHERITANCE

Question 1

Characters or Traits

Answer 1

Individual biological properties of a species

Question 2

Wild type

Answer 2

The most common form of any trait of an organism that is found “in the wild,” or in nature.

Question 3

Mutants + they arise by (2)

Answer 3

The heritable variants observed in a species that differ from wild type. Arise by from wild types by a process called mutation

Question 4

Mutation results in____ and is also known as

Answer 4

heritable changes in the DNA of a gene

The changed form of the gene

Question 5

Mutations arise by

Answer 5

mistakes in cellular processing of DNA

Question 6

Genetic dissection/Gene discovery (3)

Answer 6

1. Gene discovery starts with a “hunt” to amass mutants for the biological function under investigation. One widely used method is to treat the organism with radiation or chemicals that increase the mutation rate.
2. The test for single-gene inheritance is to mate individuals showing the mutant phenotype with wild-type individuals, and then to analyze the first and second generations of descendants. In each generation, the diagnostic ratios of plants with blue flowers to those with white flowers will reveal whether a single gene controls white versus blue flower color.
3. Other mutations affecting flower color (per- haps mauve, blotched, striped, and so on) would be ana- lyzed in the same way, resulting overall in a set of defined “flower-color genes.” Through genetics, the set of gene functions that interact to produce the trait we call flower color can be defined.

Question 7

Forward genetics

Answer 7

A strategy to understanding biological function starting with random single-gene mutants and ending with their DNA sequence and biochemical function

Question 8

Reverse genetics

Answer 8

Reverse genetics starts with genomic analysis at the DNA level to identify a set of genes as candidates for encoding the biological trait of interest, then induces mutants targeted specifically to those genes, and then examines the mutant phenotypes to see if they indeed affect the trait under study.)

Question 9

What do genes do?

Answer 9

encode proteins or RNA molecules that facilitate or regulate protein expression

Question 10

Pure lines

Answer 10

organisms with homogenous genetic constituents

Question 11

self pollination

Answer 11

allowing pollen from a flower to fall on its own stigma

Question 12

The slash shows that

Y/Y, y/y, or Y/y

Answer 12

the alleles are a pair

Question 13

Mendel’s first law or the law of equal segregation

Answer 13

In meiosis, the members of a gene pair separate equally into the cells that become eggs and sperm, the gametes. Hence, a single gamete contains only one member of the gene pair.

Question 14

zygote

Answer 14

the first cell that develops into a progeny individual

Question 15

homozygote

Answer 15

a pair of identical alleles for a given gene

Question 16

heterozygote

Answer 16

the alleles of the gene pair differ

Question 17

monohybrid

Answer 17

a heterozygote for one gene

Question 18

monohybrid cross

Answer 18

a cross of the type Y /y ×Y /y

Question 19

Somatic cell division +product (2)

Answer 19

Division of cells of the main body, known as the soma. The products of somatic cell division are exact copies of the parent cell.

Question 20

Sexual cell division (4)

Where it takes place+ what divides+ what produced in pant/fungi+alge

Answer 20

• Takes place in sex organs.
• Specialized cells called meiocytes divide to produce sex cells such as sperm and eggs in plants and animals, or sexual spores in fungi or algae

Question 21

n =

Answer 21

the number of chromosomes in the genome

Question 22

diploid (2)

Answer 22

• 2n somatic cells
• the chromosomes are in pairs

Question 23

homologous chromosomes

Answer 23

the two members of a pair (Diploid)

Question 24

haploid

Answer 24

just one chromosome set, n

Question 25

Mitosis illustrated with n and 2n

Answer 25

either 2n → 2n + 2n
or n → n + n

Question 26

Meiosis takes place only in________, and the resulting gametes are _______

Answer 26

diploid cells, and the result- ing gametes are haploid

Question 27

meiosus illustrated with 2n

Answer 27

2n → n + n + n + n

Question 28

Mitosis in diploid (3)

Answer 28

• At the onset of mitosis in somatic cells, the chromosomes condense by coiling to become shorter, and they are seen to have duplicated to form daughter units called chromatids
• Each pair of chromatids aligns on the equatorial plane of the cell and then, as the cell divides, molecular threads called spindle fibers attach to the centromere and pull one sister chromatid into each daughter cell as the centromere divides.
• Once in the daughter cells, the chromatids become individual chro- mosomes in their own right.

Question 29

S phase

Answer 29

DNA replication

Question 30

Meiosis difference than mitosis:

Answer 30

The two homologous chromosomes pair to form a group of four chromatids at the equatorial plane. In the first division, the centromere holding a pair of sister chromatids together does not divide. One pair of chromatids is pulled into each daughter cell by spindles that attach to the undivided centromeres. At the second division of meiosis, the centromeres divide; and now each chromatid is pulled into its own cell, which is now effectively haploid

Question 31

Mitosis in haploid

Answer 31

Mitosis in haploids progresses in much the same way, but in haploid organisms, each somatic cell bears only one chromosome set

Question 32

Meiosis in Haploids

Answer 32

In haploids, meiosis takes place at one special stage of the life cycle when two haploid cells unite to form a tran- sient diploid meiocyte. This cell union is a type of sexual union, although haploids generally do not have true sexes.

Question 33

What are the structural differences between wild-type and mutant alleles at the DNA level of a gene?

Answer 33

They are generally found to be identical in most of their sequences and differ only at one or several nucleotides of the hundreds or thousands of nucleotides that make up the gene.

Question 34

If the nucleotide sequence of an allele changes as the result of a rare chemical “accident,” a new mutant allele is created. Such changes can occur ____ and can be a change in ——-,—-,——

Answer 34

Such changes can occur anywhere along the nucleotide sequence of a gene. For example, a mutation could be a change in the identity of a single nucleotide, or the deletion of one or more nucleotides, or even the addition of one or more nucleotides.

Question 35

The mutational damage can occur

Answer 35

at any one of many different sites

Question 36

When is DNA replicated?

Answer 36

During S phase

Question 37

The replication of DNA during the S phase produces

Answer 37

two copies of each of the alleles A and a

Question 38

At the molecular level, the primary phenotype of a gene is

Answer 38

the protein it produces

Question 39

exons

Answer 39

The protein-coding regions of a gene

Question 40

introns

Answer 40

noncoding regions of the gene

Question 41

Most mutations that alter phenotype alter ….

Answer 41

the amino acid sequence of the gene’s protein product, resulting in reduced or absent function.

Question 42

null allele

Answer 42

the proteins encoded by them completely lack the gene’s WT/normal function

Question 43

leaky mutations

Answer 43

Mutant alleles that reduce the level of enzyme function, partial inactivation of the wildtype function. Some wild-type function seems to “leak” into the mutant phenotype.

Question 44

haplosufficient+heterozygotes (2)

Answer 44

• Although a wild-type diploid cell normally has two fully functional copies of a gene, one copy of a haplosufficient gene provides enough gene product (generally a protein) to carry out the normal transactions of the cell.
• In a heterozygote (say, +/m, where m is a null allele), the single functional copy encoded by the + allele provides enough protein product for normal cellular function.

Question 45

Recessiveness is observed in null mutations in genes that are functionally

Answer 45

haplosufficient

Question 46

haploinsufficient+ dominat?

What would be dominant?

Answer 46

In such cases, a null mutant allele will be dominant because, in a heterozygote (+/P), the single wild-type allele cannot provide enough product for normal function and the mutated allele is dominant

Question 47

As a general rule, a null mutation is —– in a haplosufficient gene, and a null mutation is — in a haploinsufficient gene.

Answer 47

recessive
dominant

Question 48

A cross between heterozygous domi- nant and wild type parents will result in a — phenotypic ratio in the progeny.

Answer 48

1:1

Question 49

The principles of inheritance (such as the law of equal segregation) can be applied in two directions:

Answer 49

1. inferring genotypes from phenotypic ratios
2. predicting phenotypic ratios from parents of known genotypes.

Question 50

Human body cells have 46 chromosomes:

Answer 50

22 homologous pairs of autosomes plus 2 sex chromosomes

Question 51

homogametic sex

Answer 51

the gametes are of only one type (ex: XX)

Question 52

heterogametic sex

Answer 52

the sex chromosomes differ (ex: XY)

Question 53

Dioecious species+ex

Answer 53

those showing animal-like sexual dimorphism, with female plants bearing flowers containing only ovaries and male plants bearing flowers containing only anthers

Question 54

hemizygous+ex

Answer 54

The differential region of the X chromosome contains many hundreds of genes; most of these genes do not take part in sexual function, and they influence a great range of human properties. The Y chromosome contains only a few dozen genes. Some of these genes have counterparts on the X chromosome, but most do not. The latter type take part in male sexual function.

Question 55

Differential region

Answer 55

The differential regions, which contain most of the genes, have no counterparts on the other sex chromosome.

Question 56

pseudoautosomal regions 1 and 2

Answer 56

The human X and Y chromosomes have two short homologous regions, one at each end. In the sense that these regions are homologous, they are autosomal like and they pair up here

Question 57

What places in the chromosome cross over in sex chromosomes?

Answer 57

pseudoautosomal regions 1 and 2

Question 58

The affected phenotype of an autosomal recessive disorder is inherited as a recessive allele; hence, the corresponding unaffected phenotype must be

Answer 58

inherited as the correspond- ing dominant allele

Question 59

the term wild type and its allele symbols are not used in ….. because…..

Answer 59

the term wild type and its allele symbols are not used in human genetics because wild type is impossible to define

Question 60

In human pedigrees, an autosomal recessive disorder is generally revealed by

Answer 60

the appearance of the disorder in the male and female progeny of unaffected parents.

Question 61

P arm

Answer 61

shorter arm

Question 62

metacentric

Answer 62

chromosome arm the same length

Question 63

Arocentric

Arocentric

Answer 63

Question 64

A full set of sister chromatids is created during the

Answer 64

S phase

Question 65

Sister chromatids have the——–, non sister chromatids can be same if —— or different if—–

Answer 65

Sister chromatids have the exact same alleles, non sister chromatids can be same if homozygote or different if heterozygote

Question 66

In autosomal dominat pedigree…..

Answer 66

there is no skipping of generation