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Pure Biology > Chapter 18 - Inheritance > Flashcards

Chapter 18 - Inheritance Flashcards

1
Q

What are hereditary traits?

A

Traits/Characteristics pass down from parent sushc as eye colour, skin tone etc

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2
Q

Define inheritance

A

Inheritance is the transmission of traits from one generation to another

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3
Q

Name the steps Mendel took conducting his experiment

A

1) Crossed tall pea plants with dwarf pea plants
2) Planted and observed the traits of the F1 generation - all were tall
3) Allowed tall plants to self feritilise and planted the seeds of the F2 generation - ratio of 3:1 (tall : short) was observed

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4
Q

What is a F1 generation?

A

Only applies to the first generation of off springs of a set of parents

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5
Q

What are doinant and recessvie traits?

A
  • Trait that always appears (e.g. F1 long stem) is D
  • Trait that always is not visible (e.g. F1 short stem) is r
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6
Q

Why should we use a large number of plants?

A

To increase accuracy

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7
Q

Why would the actual number of offspring not match the expected ratio precisely?

A

The ratio is based off of chance and probabilities due to the random nature of feritilisation

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8
Q

What are hereditary factors known as?

A

Genes. They are responsible for transmission of characteristics

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9
Q

Define genes

A

A gene is a sequence of DNA nucleotides that code for a particular protein

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10
Q

Each characteristics is controlled by…

A

A pair of factors in the cells of an organism

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11
Q

What happens if 2 factors differ?

A

The dominant factors shows effect. The 2 factors in each pair segregate during gamete formation (each gamete contains one factor) - Law of segregation

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12
Q

What does the fusion of gametes at fertilisation do?

A

Restore the diploid condition in the zygote, the zygote contains 2 factors for a particular characteristic + gametes unite at random so hat the ratio of characteristics among the offspring can be predicted

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13
Q

What are alleles?

A

The different forms of the same gene are called alleles. Alleles occupy the same relative position on a pair of homologous chromosomes

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14
Q

If someone inherits a single and double eyelid, the double eyelid is the one that is expressed. Why?

A

Double eyelid = Dominant allele
Single eyelid = Recessive allele

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15
Q

When can a recessive allele express itself?

A

When a person inherits both recessive alleles in their genes

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16
Q

What is a genotype?

A

The combination of alleles for a particular gene

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17
Q

What is a phenotype?

A

The expressed trait or outward appearance

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18
Q

Match the genotypes and phenotypes:
Genotypes: DD, Dd, dd
Phenotypes: Double eyelids & single eyelids

A

DD –> Double eyelids
Dd –> Double eyelids
dd –> Single eyelid

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19
Q

What is homozygous?

A

Havin 2 identical alleles of a particular gene (e.g. DD, dd)

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20
Q

What is heterozygous?

A

Having 2 different alleles of a particular gene (e.g. Dd)

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21
Q

What is homozygous dominant?

A

Has 2 dominant alleles for the gene (e.g. DD)

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22
Q

What is homozygous recesive?

A

Has 2 recessive alleles for the gene (e.g. dd)

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23
Q

Describe a genetic diagram

A
  1. Parental Phenotype (pure bred)
  2. Parental Genotype
    - Cell reduction occurs
    - Separates a pair of alleles by splitting each pair of homologus chromosomes
    - Each gamete only receives one copy of each allele
  3. Gametes
  4. F1 genotypes
  5. F1 phenotypes
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24
Q

What do you use when you want to find out the genotype of an organism showing the dominant characteristic?

A

A test cross

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25
If a plant is homozygous, all offsprings are tall. But if a plant is heterozygous, offsprings will be in what ratio?
Tall : Dwarf 1 : 1
26
What is codominance?
In codominance, both alleles express themselves in the heterozygote, which has a phenotype intermediate between that of its pure bred parents. The alleles are said to be codominant
27
What are multiple alleles?
A gene that exists in more than 2 different forms has multiple alleles
28
How many alleles can an individual have?
2, 1 from each parent
29
Which blood group exhibits codominance?
Blood group AB. Alleles are IA and IB
30
Which blood groups are dominant and which are recessive?
IA and IB are dominant over IO
31
What is the genotype for people with blood group A, B, AB and O?
A: IA IA / IA IO B: IB IB / IB IO AB: IA IB O: IO IO
32
How many sex and non sex chromosomes are there in a human?
Sex: One pair Non-sex: 22 pairs
33
What are non sex chromosomes called?
Autosomes
34
Each human has one pair of each type of chromosome. Hence, human cells are diploid with __ pairs of chromosomes
23
35
How are the sex chromosomes different in males and females?
Males: The pair of sex chromosomes consists of one X chromosome and one shorter Y chromosome Females: Pair of X chromosomes in each cell
36
What is the chance of an offspring being male or female?
50/50 chance, equal chance, 1:1 chance
37
How many chromosomes are there in a male?
44 non sex + X + Y
38
How many chromosomes are there in a female?
44 non sex + X + X
39
How many chromosomes are there in male gametes (sperm) ?
22 non sex + X OR 22 non sex + Y
40
How many chromosomes are there in female gametes?
22 non sex + X
41
What are the results of the fusion of gametes?
22 + 22 = 44 autosomes X + X = girl baby (XX) X + Y = boy baby (XY)
42
Define variation
Variation refers to the differences in traits between individuals of the same species
43
What are some examples of traits showing discontinuous variation? (Mendel)
- The traits show clear cut phenotypes with no intermediate forms between the traits - In Mendel's experiment, the seeds of the pea plant were either green or yellow or either smooth or wrinkled
44
What are some examples of traits showing discontinuous variation? (Blood)
- Traits are easily distinguishable and are not affected by environmental conditions - ABO blood groups, double or single eyelids, ability to roll tongue
45
What are some examples of continuous variation?
- Greater exposure to sunlight causes one to have darker skin - Height, shoe size, body type
46
What are some differences between discontinuous and continuous variation?
1) D involves a few clear cut phenotypes (e.g. green or yellow in pea plants) while C involves a range of phenotypes (e.g. human skin colour) 2) D controlled by one or a few genes while C is controlled by many genes 3) D does not show additive effect while C shows additive effect 4) D is relatively unaffected by environmental conditions while C is greatly affected by environmental conditions
47
What are the 3 sources of genetic variation?
1) Meiosis 2) Random fertilisation 3) Mutation
48
What does meiosis produce?
Genetically dissimilar gametes with different combinations of parental chromosomes resulting in genetically different offsprings
49
What happens during random fertilisation?
Any one off the million sperms released can randomly fuse with an egg to form a unique zygote. As each gamete is unique, the offspring produced from the fusion of gametes will be genetically different
50
What happens during mutation?
Genes are usually passed onto another generation unchanged. Before a cell divides, the chromosomes replicate or divide the genes they carry are copied exactly. Hereditary depends on accurate replication. Occasionally an error may occur an the gene may be modified or the chromosome altered resulting in mutation
51
Define mutation
Change in the sequence of gene or in chromosome number
52
What does gene mutation cause?
- Diversity within species - Variation between individuals (as it results in new alleles in genes)
53
What happens if mutation occurs during gamete production?
The resulting genetic change can be inherited by the offspring
54
What is chromosome mutation?
The change in number of chromosomes in an organism
55
Can mutations be inherited?
Yes
56
What are 2 examples of gene mutation?
1) Sickle cell anemia 2) Albinism
57
Describe albinism
- Recessive gene mutation - Homozygous for albinism allele are albinos - Absence of pigment in hair, skin, eyes etc - Eyes are red due to blood vessels - Sensitive to sunlight and skin burn easily
58
Describe sickle cell anaemia
- Results in change in the structure of gene - Homozygous recessive - Change in the sequence of bases or nucleotides in DNA - HbS is almost the same as regular haemoglobin except in one amino acid causing the 3D shape to change and clump together - Loses ability to transport oxygen, fragile, sticky, get stuck in narrow blood vessels, slowing/blocking flow of oxygen to parts of the body - Can be fatal
59
What is an example of chromosome mutation?
Humans normally have 46 chromosomes. Some have one extra --> Usually fails to develop, exception is the zygote with an extra copy of chromosome 21 aka Down Syndrome
60
Describe how Down Syndrome comes about
- Each normal body cell has 2 copies of chromosome 21 - Each sperm has one copy of chromosome 21 - The egg has 2 copies of chromosome 21 and chromosome 21 is absent in the other egg - Fertilisation occurs and the zygote has 3 copies of chromosome 21 and will develop into a child with Down Syndrome
61
What increases the chance of the copies of chromosome 21 not separating during gamete formation?
The older the mothers age.
62
Can an extra copy of chromosome only happen in eggs?
It is also possible for a mutation to occur in the sperm resulting in a sperm that carries an extra chromosome 21
63
What are mtuagens?
Presence of certain agents in the external environment that increases the rate of mutation greatly
64
What are some examples of mutagens?
- Ionising radiation e.g. UV light, radiations are mutagenic - Some chemicals, if present in certain concentrations are mutagenic - Tar, chemicals in cigaratte smoke and drugs
65
Define natural selection
Natural selection refers to a process in which organisms with desirable genes and characteristics are 'selected' or 'favoured' to survive and pass on their genes to their offspring
66
How do organisms become adapted?
Mutation provides new genes or alleles for natural selection to operate on. After thousands of years, more beneficial qualitites (genes or alleles) may accumulate in a species. The new breed of organisms may be better adapted to their new environment. They may even change so much that they become a new species
67
Define evolution
The gradual change in the inheritable characteristics of a population over time
68
Describe how mutation, competitions and natural selection leads to evolution
1) Spontaneuous muation occurs, produces variety of colour/size of rabbits 2) Rabbits migrate to 2 diff env (dense forest and open plains) 3) Competition among them occurs --> survival of the fittest 4) Nature selects varieties with favourable genes/characteristics best fitted to survive 5) Other varieties die/decrease (competition for food/diseases/predation) 6) Those that survive reproduce and pass down the favourable genees to offspring who become predominant in the env
69
How do rabbits in the dense forest adapt?
1) Fark coloured fur camoflages well in dark forest 2) Small size and crouching, less easily detectable by predators 3) Hide in crevices or among logs
70
How do rabbits in the open plain adapt?
1) Light coloured coat, camouflages well in open plains 2) Large size and long hind legs allow it to run faster and escape from predators 3) Long ears gives it a keener sense of hearing to detect predators 4) Upright position allows farther sight, for food and for approach of predators

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