Chapter 17

Question 1

inheritance

Answer 1

the transmission of genetic information from generation to generation

Question 2

chromosome

Answer 2

a thread-like structure of DNA, carrying genetic information in the form of genes

Question 3

gene

Answer 3

a length of DNA that codes for a protein

Question 4

allele

Answer 4

a version of a gene

Question 5

Describe the inheritance of sex in humans with

reference to XX and XY chromosomes

Answer 5

The female gamete (egg) has only an X chromosome. That is why there will always be a X in XX and XY. However, the male gamete (sperm) has either an X or Y chromosome. Around 50% of sperm cells have an X chromosome and 50% a Y chromosome, therefore there is a 50% chance of having either a boy or girl, when paired with a X chromosome.

Question 6

the sequence of bases in a gene

Answer 6

The genetic code for putting together amino acids in the correct order to make a specific protein.

Question 7

Explain that DNA controls cell function by controlling the production of proteins (some of which are enzymes), antibodies and receptors for neurotransmitters

Answer 7

The body has to go through many different chemical reactions in order to function. Many of the substances responsible for allowing these chemical reactions to occur (or simply speeding them up) are proteins. Which the DNA codes for with its sequence of bases.

Question 8

Explain how a protein is made

Answer 8

The DNAs gene coding for a protein is found and remains in the nucleus throughout this process. The mRNA molecules carry a copy of the gene to the cytoplasm where the mRNA passes through ribosomes. Of which, assembles the amino acids into protein molecules. The specific order of amino acids is determined by the sequence of bases in the mRNA.

Question 9

Explain how the DNA are the same in the whole body, but we have different organs and features

Answer 9

All body cells in an organism contain the same genes, but many genes in a particular cell are not expressed because the cell only makes the specific proteins it needs

Question 10

haploid nucleus

Answer 10

a nucleus containing a single set of unpaired chromosomes, e.g. in gametes

Question 11

diploid nucleus

Answer 11

a nucleus containing two sets of chromosomes, e.g. in body cells

Question 12

Explain the difference between a diploid cell and a human diploid cell

Answer 12

In a diploid cell, there is a pair of each type of chromosome and in a human diploid cell there are 23 pairs

Question 13

mitosis

Answer 13

nuclear division giving rise to genetically identical cells

Question 14

State the role of mitosis

Answer 14

Mitosis is responsible for growth, the repair of damaged tissues, the replacement of cells and asexual reproduction.

Question 15

The exact duplication of chromosomes occurs…

Answer 15

…before mitosis

Question 16

Explain how the chromosome number is kept the same after mitosis

Answer 16

The chromosomes in the nucleus are copied before mitosis. When the cell goes through the process of mitosis, the copies of chromosomes separate from the originals, maintaining the chromosome number.

Question 17

Stem cells

Answer 17

unspecialised cells that divide by mitosis to produce daughter cells that can become specialised for specific functions.

Question 18

meiosis

Answer 18

reduction division in which the chromosome number is halved from diploid to haploid resulting in genetically different cells

Question 19

State what meiosis is involved in

Answer 19

the production of gametes

Question 20

Explain how meiosis produces variation

Answer 20

It produces variation by forming new combinations of maternal and paternal chromosomes.

Question 21

genotype

Answer 21

the genetic make-up of an organism in terms of the alleles present

Question 22

phenotype

Answer 22

the observable features of an organism

Question 23

homozygous

Answer 23

having two identical alleles of a particular gene

Question 24

pure-breeding

Answer 24

when two identical homozygous breed together; a heterozygous individual can never be pure-breeding

Question 25

heterozygous

Answer 25

having two different alleles of a particular gene

Question 26

dominant

Answer 26

an allele that is expressed if it is present

Question 27

recessive

Answer 27

an allele that is only expressed when there is no dominant allele of the gene present

Question 28

pedigree diagrams

Answer 28

you don’t need to know shit about this but you do need to be able to interpret it for the inheritance of a specific characteristic.

Question 29

genetic diagrams

Answer 29

• use to credit monohybrid crosses
• calculate phenotypic ratios (limited to 1:1 and 3:1)
• not something you need to know but a friendly reminder to read the question in case they pull a ‘out of boys….’ bullshit.

Question 30

punnett squares

Answer 30

turns out what you might think are genetic diagrams are actually punnet squares.

Question 31

how to use a test cross to identify an unknown genotype

Answer 31

You can not really identify dominant genotypes as they are either Tt or TT. Therefore, we use a test cross. We mate the animal or plant with a recessive homozygous animal or plant. If the organism was TT, then all of the offspring would be Tt, meaning their phenotype would be dominant. However, if they were Tt, then at least half of the offspring would be a recessive phenotype.

Question 32

Explain codominance

Answer 32

Sometimes, both alleles in an organism are neither recessive or dominant. So what can occur is that the phenotype is a mixture of the effects of each allele. For example, in blood groups (btw I-O is “recessive” to I-A and I-b) we can have simple forms like I-A and I-A to form the blood group A, however there can also be a mixture like I-A and I-B to form the blood group AB.

Question 33

sex-linked characteristic

Answer 33

a characteristic in which the gene responsible
is located on a sex chromosome and that this makes it more common in one sex than in the other. For example, colour blindness (+ blood clotting), the Y chromosome is pretty much useless so males rely on the characteristic of their X chromosome to decide some of their features. In this case, an allele of a gene does not produce the protein necessary for colour vision. However, it is recessive. Therefore, women are less likely to get it with the chromosome X-R X-r. However, males only have 1 X chromosome; meaning they could be colour blind with X-r Y.