Lab 5

Question 1

autosomal chromosomes (autosomes)

Answer 1

• 22 pairs
• The autosomal chromosomes carry genes that affect somatic characteristics (such as hair color)
• Each pair of autosomal chromosomes has the same structure and carries genes that affect the same characteristics.

Question 2

sex chromosomes

Answer 2

• 1 pair
• The sex chromosomes are responsible for determining the genetic sex of an individual.
• there is an X chromosome and a Y chromosome
• Females have XX chromosomes and males have XY
• Y chromosome is very small compared to the X chromosome
• Y is responsible primarily for determining the sex of an individual.
• X chromosome carries a large number of genes, many of which are not concerned with sex determination.

Question 3

karyotype

Answer 3

• an individual’s collection of chromosomes
• photograph a cell during mitosis, enter the photograph into a computer for analysis and electronically arrange the chromosomes into pairs according to size and the position of the centromere.
• usually prepared from a cell during metaphase of mitosis
• allows for the detection of many chromosomal abnormalities
• arranged according to deceasing size.
• Individual chromosomes may be further identified by the position of the centromere.

Question 4

Three terms are used to describe the various centromere locations:

Answer 4

i) metacentric - the centromere is located in the middle of the chromosome
ii) subterminal - the centromere is located between the middle and the end of the chromosome
iii) acrocentric - the centromere is located very close to one end of the chromosome

Question 5

Trisomy 21

Answer 5

• a chromosomal condition also known as Down Syndrome.
• 3 copies of chromosomes 21 rather than two
• arises when the chromosomes fail to separate properly during meiosis called nondisjunction

Question 6

nondisjunction

Answer 6

• arises when the chromosomes fail to separate properly during meiosis
• can occur when homologous chromosomes fail to separate in Anaphase I and both members of a pair go to one pole
• meiosis II where the sister chromatids fail to separate in Anaphase II and both chromatids go to one pole
• during both Ana I [leads ti irregular # of chromo in all 4 gametes]
• during Ana II [irrecular # on chromo in just 2 out of 4 of the gametes])

Question 7

Non-disjunction examples:

Autosomal and sexlinked

Answer 7

Autosomal Chromosomes:

• Trisomy 21 (Down syndrome)
• Trisomy 13 (Patau syndrome)
• Trisomy 18 (Edward’s syndrome).

Sex Chromosomes:

• Turner’s syndrome, a female with only one X chromosome.
• Klinefelter’s syndrome, a male having the sex chromosome complement XXY.

Question 8

Cri-du-chat syndrome

Answer 8

is associated with the loss of about one half of the short arm of one member of the homologous pair for chromosome 5.

Question 9

phenylketonuria (PKU)

Answer 9

results when the liver enzyme, phenylalanine hydroxylase is lacking. The amino acid phenylalanine accumulates and has serious detrimental effects on the developing brain of a newborn. The condition can be detected by the analysis of an infant’s blood, done routinely at birth. If the condition is detected, a strict diet low in phenylalanine is instituted and central nervous system development proceeds normally.

Question 10

Genetic disorders can be caused by:

Answer 10

• inborn errors of metabolism due to recessive alleles. This involves production of a defective enzyme or the complete absence of an enzyme required for some important chemical reaction in the cell.
• gain or lose a piece of a chromosome
• some gametes have extra chromosomes while some will be missing them.

Question 11

inborn errors of metabolism due to recessive alleles examples

Answer 11

PKU phenylketonuria
•results when the liver enzyme, phenylalanine hydroxylase is lacking. The amino acid phenylalanine accumulates and has serious detrimental effects on the developing brain of a newborn. The condition can be detected by the analysis of an infant’s blood, done routinely at birth. If the condition is detected, a strict diet low in phenylalanine is instituted and central nervous system development proceeds normally.

albinism
•due to a missing enzyme needed to produce the pigment melanin

Question 12

Locus

Answer 12

The position of a gene on a chromosome.

Question 13

Genotype

Answer 13

The genetic constitution of an organism, i.e. the actual genes present on the chromosomes of an individual, eg. AA, Aa, aa

Question 14

Phenotype

Answer 14

The observed characteristics of an individual; the physical expression of a gene, eg. blue
eyes.

Question 15

Alleles

Answer 15

Alternate forms of the same gene (e.g. A and a) found at the same locus on homologous chromosomes, affecting the same characteristic yet often coding for different phenotypes.

Question 16

Dominant allele

Answer 16

An allele which needs to be present on only one of the two homologous chromosomes in order to be expressed; in other words, an allele which masks the expression of alternative alleles. By convention, the dominant allele is usually represented by a capital letter (A). Thus AA and Aa are phenotypically identical since the dominant allele A masks the alternative allele a.

Question 17

Recessive allele

Answer 17

An allele which must be present on both members of a pair of homologous chromosomes in order to be expressed (aa). Recessive alleles are written with lower case letters. In the heterozygous condition (Aa), the recessive allele is masked by the dominant allele.

Question 18

Homozygous

Answer 18

Refers to the presence of identical alleles on homologous chromosomes (e.g. AA or aa).

Question 19

Heterozygous

Answer 19

Refers to the presence of unlike alleles on homologous chromosomes (e.g. Aa).

Question 20

First Filial (F1) Generation

Answer 20

The offspring resulting from the crossing of individuals of the parental generation.

Question 21

Second Filial (F2) Generation

Answer 21

The offspring resulting from crossing members of the Fl generation among themselves.

Question 22

Monohybrid cross

Answer 22

Examines the inheritance of a single trait.

eg. Parental genotype could be: AA – gametes formed by meiosis have only A
Aa – ½ gametes are A, ½ gametes are a
aa – gametes have only a

Question 23

Dihybrid cross

Answer 23

Examines the inheritance of 2 different traits located on 2 different pairs of homologous chromosomes. These genes sort independently of each other.

eg. Parental genotype could be:
AABB – gametes formed by meiosis have only AB
aabb – gametes have only ab
AaBB – ½ gametes are AB, ½ gametes are aB
AaBb – ¼ gametes are AB, ¼ gametes are Ab, ¼ gametes are aB, ¼ gametes are ab

Question 24

Simple dominant - recessive inheritance

Answer 24

The phenotype of an individual reflects the interaction between a single pair of alleles

Question 25

Incomplete dominance

Answer 25

• both alleles contribute to the phenotype of the organism, as neither allele completely masks the expression of the other.
• a hybrid intermediate between the two original traits is often produced

Ex: crossing a red-flowering plant with a white-flowering plant produces a pink-flowering plant
Ex: Humans- the sickle cell trait
aa: abnormal hemoglobin RBC sicle shaped = severe anemia
Aa - half of their hemoglobin is normal and half is not, so they have a more minor problem with anemia

Question 26

Multiple-allele inheritance

Answer 26

• Genes exhibit more than two alternate forms such as in the inheritance of ABO blood types.

• Three alleles of a single gene, called the I gene - IA, IB, and i, determine the four blood types found in humans.
• We each received two of these alleles.
• A/B co dominant, i recessive

Question 27

Polygenic Inheritance

Answer 27

• Poylgentic traits = depend on the interactions of several different gene pairs
• multiple alleles act together to influence a characteristic, there can be considerable variation in the resulting phenotype

Ex: Human skin color, height, eye color and hair color

Question 28

Sex-linked Inheritance

Answer 28

• Genes carried on the X chromosome are said to be sex-linked (or X-linked).
• recessive sex-linked gene is expressed in males when only one allele is present (male only has a single X chromosome).
• Sex-linked characteristics in females are inherited like other traits, since a female has two X chromosomes and will not express the condition if heterozygous for the trait.

Ex: Red-green color blindness and hemophilia

Question 29

Missing a piece of chromo 5

Answer 29

Missing a piece of chromo 5 - Cri-Du-Chat syndrome

Autosomal Abnormalities:

Question 30

X (Female with one X)

Answer 30

X (Female with one X) - Turner’s Syndrome

Sex Linked Abnormality:

Question 31

Having extra chromo 13

Answer 31

Having extra chromo 13 - Patau syndrome

Autosomal Abnormalities:

Question 32

Having extra chromo 18

Answer 32

Having extra chromo 18 - Edward’s Syndrome

Autosomal Abnormalities:

Question 33

Having extra chromo 21

Answer 33

Having extra chromo 21 - Down syndrome

Autosomal Abnormalities:

Question 34

XXY (male with extra sex chromo)

Answer 34

XXY (male with extra sex chromo) - Klinefelter’s Syndrome

Sex Linked Abnormality: