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biology > chapter 6: chromosomes + genomes > Flashcards

chapter 6: chromosomes + genomes Flashcards

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1
Q

What are chromosomes made of?

A
  • are made of DNA organised in genes
  • chromosomes are thread like structures that store DNA
  • dna storage devices
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2
Q

What is the structure of DNA?

A
  • DNA is a chemical that contains a code to make proteins
  • double-stranded and made of nucleotides - bases
  • double helix structure
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3
Q

What are the bases (nucleotides) in DNA?

A
  • adenine
  • guanine
  • cytosine
  • thymine
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4
Q

Define gene

A

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

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5
Q

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

A
  • 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
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6
Q

What is the genome?

A

all of an organism’s genetic material

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7
Q

How many genes are in the human genome?

A

around 20,000-25,000

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8
Q

What else makes up our DNA?

A

non-coding regions

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9
Q

How many chromosomes do humans have?

A

46 chromosomes per cell

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10
Q

How many autosomes do humans have?

A

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

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11
Q

What are the male sex chromosomes?

A

XY

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12
Q

What are the female sex chromosomes?

A

XX

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13
Q

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

A
  • 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
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14
Q

How many homologous pairs of chromosomes do humans have?

A
  • males have 22 pairs
  • females have 23 pairs
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15
Q

what are homologous chromosomes

A

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

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16
Q

What is the ‘waist’ of a chromosome called?

A

centromere

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17
Q

Draw and name the 4 shapes of chromosome?

A

telocentric

acrocentric

submetacentric

metacentric

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18
Q

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

A
  • 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
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19
Q

What 3 features are used to identify homologous chromosomes?

A
  • size (length)
  • shape (centromere position- metacentric etc.)
  • banding pattern
20
Q

In what order are chromosomes lined up in a karyotype?

A

from largest to smallest

21
Q

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

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

klinefelter’s syndrome - XXY

down syndrome- 3 chromosome 21

patau syndrome- 3 chromosome 13

22
Q

What cells are diploid?

A

all cells except sex cells and red blood cells

23
Q

What does diploid mean?

A

2 copies of each chromosome
denoted by 2n

24
Q

What cells need to be haploid? Why?

A
  • 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
25
Q

what is meiosis

A

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

26
Q

what is a haploid

A

denoted by n
half of the chromosomes of a somatic cell

27
Q

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

A

once

28
Q

How many divisions are there in meiosis?

A

two

29
Q

How many daughter cells result from one round of meiosis?

A

2 genetically different haploid daughter cells

30
Q

Outline what occurs in interphase

A

interphase:

  • DNA is replicated
  • produces x-shaped chromosomes (before they were single-stranded and not joined)- consists of sister chromatids joined at the centromere
31
Q

Outline what occurs in prophase I

A

prophase I

  • chromosomes condense
  • the nuclear membrane breaks down
  • spindles form
  • crossing over occurs
32
Q

Outline what occurs in metaphase I

A

metaphase I

  • homologous chromosome pairs line up next to each other along the equator of the cell.
33
Q

Outline what occurs in anaphase I

A

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
34
Q

Outline what occurs in telophase I

A

telophase I

  • nuclear membrane reforms around each set of chromosomes
  • spindle fibres disappear
  • cytokinesis occurs
35
Q

Outline what occurs in prophase II

A

prophase II

  • chromosomes may condense if necessary
  • nuclear membrane breaks down
36
Q

Outline what occurs in metaphase II

A

metaphase II

  • chromosomes line along the equator of the cell
37
Q

Outline what occurs in anaphase II

A

anaphase II

  • sister chromatids separate and are pulled to opposite poles
  • separated chromatids are now individual chromosomes
38
Q

Outline what occurs in telophase II

A

telophase II

  • nuclear membrane forms around the groups of chromosomes
  • spindles disappear
  • cytokinesis occurs resulting in four haploid gamete cells
39
Q

What is independent assortment

A

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

40
Q

what is crossing over

A
  • an event that occurs in prophase I
  • INVOLVES THE EXCHANGE OF CORRESPONDING SEGMENTS OF DNA BETWEEN HOMOLOGOUS CHROMOSOMES
41
Q

what are karyotypes and their purpose

A
  • 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.
42
Q

potential chromosome abnormalities

A
  • 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.
43
Q

how chromosomal abnormalities can occur

A

nondisjunction:

  • two copies of the same chromosome fail to separate to opposite poles of the spindle during anaphase
44
Q

difference between trisomy and monosomy

A

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.
45
Q

what is sexual reproduction

A
  • involves the fusion of two gametes and requires two parents
  • the offspring produced differ genetically from each other and also from their parents.
46
Q

what happens when meiosis goes wrong

A

non disjunction -> monosomy or trisomy

biology (8 decks)

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