chapter 6: chromosomes + genomes

Question 1

What are chromosomes made of?

Answer 1

• are made of DNA organised in genes
• chromosomes are thread like structures that store DNA
• dna storage devices

Question 2

What is the structure of DNA?

Answer 2

• DNA is a chemical that contains a code to make proteins
• double-stranded and made of nucleotides - bases
• double helix structure

Question 3

What are the bases (nucleotides) in DNA?

Answer 3

• adenine
• guanine
• cytosine
• thymine

Question 4

Define gene

Answer 4

section of a DNA on a chromosome that codes for specific proteins that control a characteristic or trait of an organism

Question 5

How is an allele different to a gene? Provide an example.

Answer 5

• alleles are versions of the genes that make you unique
• they code for a trait for but contain different sequences of bases causing the traits to be expressed differently (different hair colours)
• alleles have the same genes but different base sequences
• eg eye colour- blue, black, brown
• hair colour- blonde black brown

Question 6

What is the genome?

Answer 6

all of an organism’s genetic material

Question 7

How many genes are in the human genome?

Answer 7

around 20,000-25,000

Question 8

What else makes up our DNA?

Answer 8

non-coding regions

Question 9

How many chromosomes do humans have?

Answer 9

46 chromosomes per cell

Question 10

How many autosomes do humans have?

Answer 10

22 pairs (44 chromosomes)
- autosomes are the chromosomes that don’t determine your sex
- they are homologous chromosomes that are identical in appearance in both males and females

Question 11

What are the male sex chromosomes?

Answer 11

XY

Question 12

What are the female sex chromosomes?

Answer 12

XX

Question 13

Is a person with the sex chromosomes XXY male or female? Why?

Answer 13

• they are male
• this is because the presence of the Y chromosomes determines that they are male
• thus the absence of the Y chromosome means that the person’s sex is female

Question 14

How many homologous pairs of chromosomes do humans have?

Answer 14

• males have 22 pairs
• females have 23 pairs

Question 15

what are homologous chromosomes

Answer 15

homologous chromosomes are pairs of chromosomes that contain the same genes at the same position (loci)

Question 16

What is the ‘waist’ of a chromosome called?

Answer 16

centromere

Question 17

Draw and name the 4 shapes of chromosome?

Answer 17

telocentric

acrocentric

submetacentric

metacentric

Question 18

What is the relationship between the complexity of an organism and the number of genes and chromosomes it has?

Answer 18

• there is no relationship between the complexity of an organisms and the number of genes and chromosomes it has
• it varies from species to species
• chromosomes in an individual can vary in size and shape
• number of genes on chromosomes varies (there are non-coding DNA on chromosomes)
• size, shape and number of chromosmes varies between species

Question 19

What 3 features are used to identify homologous chromosomes?

Answer 19

• size (length)
• shape (centromere position- metacentric etc.)
• banding pattern

Question 20

In what order are chromosomes lined up in a karyotype?

Answer 20

from largest to smallest

Question 21

What are 3 things that can be identified using a karyotype?

Answer 21

• sex
• number of chromosomes (numbers)
• broken chromosomes (any missing pieces)

klinefelter’s syndrome - XXY

down syndrome- 3 chromosome 21

patau syndrome- 3 chromosome 13

Question 22

What cells are diploid?

Answer 22

all cells except sex cells and red blood cells

Question 23

What does diploid mean?

Answer 23

2 copies of each chromosome
denoted by 2n

Question 24

What cells need to be haploid? Why?

Answer 24

• sex cells need to be haploid
• so that when the 2 gametes (one from each parent) fuses, the zygote will be diploid and have 46 chromosomes
• occurs to ensure that chromosome numbers remain constant from one generation to the next

Question 25

what is meiosis

Answer 25

Meiosis is the process that produces gametes with the haploid number of chromosomes

Question 26

what is a haploid

Answer 26

denoted by n half of the chromosomes of a somatic cell

Question 27

How many times is DNA replicated in the process of meiosis?

Answer 27

once

Question 28

How many divisions are there in meiosis?

Answer 28

two

Question 29

How many daughter cells result from one round of meiosis?

Answer 29

2 genetically different haploid daughter cells

Question 30

Outline what occurs in interphase

Answer 30

interphase: - DNA is replicated - produces x-shaped chromosomes (before they were single-stranded and not joined)- consists of sister chromatids joined at the centromere

Question 31

Outline what occurs in prophase I

Answer 31

prophase I - chromosomes condense - the nuclear membrane breaks down - spindles form - crossing over occurs

Question 32

Outline what occurs in metaphase I

Answer 32

metaphase I - homologous chromosome pairs line up next to each other along the equator of the cell.

Question 33

Outline what occurs in anaphase I

Answer 33

anaphase I - the homologous chromosome are separated from each other and pulled to opposite poles through the contraction of the spindles - the sister chromatids DO NOT separate

Question 34

Outline what occurs in telophase I

Answer 34

telophase I - nuclear membrane reforms around each set of chromosomes - spindle fibres disappear - cytokinesis occurs

Question 35

Outline what occurs in prophase II

Answer 35

prophase II - chromosomes may condense if necessary - nuclear membrane breaks down

Question 36

Outline what occurs in metaphase II

Answer 36

metaphase II - chromosomes line along the equator of the cell

Question 37

Outline what occurs in anaphase II

Answer 37

anaphase II - sister chromatids separate and are pulled to opposite poles - separated chromatids are now individual chromosomes

Question 38

Outline what occurs in telophase II

Answer 38

telophase II - nuclear membrane forms around the groups of chromosomes - spindles disappear - cytokinesis occurs resulting in four haploid gamete cells

Question 39

What is independent assortment

Answer 39

is the formation of random chromosome combinations IN GAMETES due to the way homologous chromosomes line up in metaphase.

Question 40

what is crossing over

Answer 40

- an event that occurs in prophase I - INVOLVES THE EXCHANGE OF CORRESPONDING SEGMENTS OF DNA BETWEEN HOMOLOGOUS CHROMOSOMES

Question 41

what are karyotypes and their purpose

Answer 41

- they are an image of chromosomes from a cell arranged in an organised manner - enables any abnormality in either number or structure of the chromosomes to be quickly identified.

Question 42

potential chromosome abnormalities

Answer 42

- changes in the total number of chromosomes - down syndrome (trisomy 21) - changes involving part of one chromosome - deletion or duplication of part of chromosome - changed arrangements of chromosomes - the location of a chromosome segment is altered and becomes relocated to a new region within the karyotype.

Question 43

how chromosomal abnormalities can occur

Answer 43

nondisjunction: - two copies of the same chromosome fail to separate to opposite poles of the spindle during anaphase

Question 44

difference between trisomy and monosomy

Answer 44

**trisomy:** three copies of a chromosome occur **monosomy:** one copy of a particular chromosome that is normally present as a homologous pair - Monosomy causes embryonic death, except for monosomy involving the sex chromosomes.

Question 45

what is sexual reproduction

Answer 45

- involves the fusion of two gametes and requires two parents - the offspring produced differ genetically from each other and also from their parents.

Question 46

what happens when meiosis goes wrong

Answer 46

non disjunction -> monosomy or trisomy