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TH- Mendel Inheritance Flashcards

1
Q

what is a trait?

A

a distinguishing quality or characteristic

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2
Q

State the 4 advantages of using peas for the genetic study

A

1- many varieties
2-mating can be controlled
3-each pea plant has sperm and egg producing organs
4-cross pollination can take place

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3
Q

What is true breeding?

A

parents would produce offspring that would carry the same phenotype, hence parents are homozygous for traits

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4
Q

What is hybridization?

A

mating or crossing of 2 true-breeding parents

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5
Q

What are alleles?

A

alternative forms of a gene

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6
Q

State the 4 concepts of Mendel’s Model

A

1- alternative versions of genes account for variations in inherited characters. i.e. alleles
2-for each character, an organism inherits two copies (that is, two alleles) of a gene, one from each parent
3-if the two alleles at a locus differ, then one, the dominant allele, determines the organism’s appearance; the other, the recessive allele, has no noticeable effect on the organism’s appearance.
4- Law of segregation

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7
Q

Describe Law of Segregation

A

The two alleles for a heritable character segregate (separate from each other) during gamete formation and end up in different gametes. Thus, an egg or a sperm gets only one of the two alleles that are present in the somatic cells of the organism making the gamete.

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8
Q

What is a homozygote?

A

organism with identical alleles

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9
Q

what is heterozygote?

A

organism with different alleles

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10
Q

what does it mean to be homozygous?

A

identical alleles

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11
Q

what does it mean to be heterozygous?

A

different alleles

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12
Q

what is phenotype?

A

appearance or observable traits

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13
Q

what is genotype?

A

genetic make up

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14
Q

what is a test cross and why is it done?

A

it is breeding an organism of unknown genotype with recessive homozygous
it is done to determine genotype of unknown

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15
Q

what are monohybrids?

A

they are heterozygous for one single character

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16
Q

what is a monohybrid cross?

A

cross between heterozygous

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17
Q

what are dihybrids?

A

heterozygous for 2 different characters

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18
Q

what is a character?

A

heritable feature that varies among individuals

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19
Q

Describe law of independent assortment

A

Genes for different traits assort independent of each other during gamete formation as the chromosomes aligning at the metaphase plate is a random procedure hence any chromosome combination is possible

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20
Q

What is the multiplication rule?

A

the probability of two (or more) independent events occurring together can be calculated by multiplying the individual probabilities of the events.
eg. probability of egg having dominant allel is 1/2 and that sperm will have dominant is 1/2 so 1/2 x 1/2 = 1/4 probability of offspring having dominant.

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21
Q

what is the addition rule?

A

rule that states that the probability of the occurrence of mutually exclusive events is the sum of the probabilities of the individual events.

22
Q

What is incomplete dominance?

A

neither allele is completely dominant and F1 hybrids have phenotypes somewhere between the 2 parental varieties.

23
Q

why does incomplete dominance not provide evidence for blending hypothesis?

A

in the F2 generation we see that there is a ratio of 1:2:1 which confirms that alleles are heritable characters.

24
Q

what is codominance?

A

both phenotypes are dominant, but cannot be expressed at the same time.

25
When is a allele called dominant?
when it is seen in the phenotype
26
describe Tay-Sachs disease
- inherited disease | - brain cells of a child cant metabolize lipids due to a crucial enzyme missing
27
who does the Tay-Sachs disease affect?
people homozygous for that allele
28
what is Pleiotropy?
when a gene at a given locus affects multiple phenotypic traits
29
What is Epistasis?
when genes at one locus affects the expression of genes at another locus. labrador example
30
What is quantitative characters?
vary in a population along a continuum
31
What is polygenic inheritance?
when 2 or more genes affect a single phenotypic character and they are quantitative eg height.
32
What is multifactorial?
many factors both genetic and environmental affect phenotype.
33
what is a pedigree?
genetic representation of a family tree that diagrams the inheritance of a trait or disease though several generations.
34
What are carriers?
heterozygotes that don't display the trait but can pass the recessive allele to their offsprings
35
How do people get recessive disorders?
both their parents are carriers or both are homozygous for the recessive allele (if it doesn't cause sterility) or one is a carrier and the other is a homozygote.
36
who are more likely to produce offsprings homozygous for recessive alleles?
if man and woman are close relatives the likeliness of passing a inherited disorder increases
37
what is consaguineous?
people descended from the same ancestor
38
what does cystic fibrosis do and how does it affect the human body?
- A normal allele codes for a membrane protein that helps in the transport of chloride ions between the cell and extracellular fluid - however recessive homozygotes have defective chloride channels or the channels are absent causing a build up of chloride inside the cell - this build up results in the cell taking up water via osmosis - this leads to the mucus around some cells to become thicker and stickier which caused many pleiotropic effects such as poor absorption of nutrients, bronchitis and more
39
how are the recessive homozygotes with sickle-cell disease affected ?
- when oxygen content in blood is low sickle-cell haemoglobin cluster into long fibres that cause the sickle cell shape of the red blood cell - this leads to various symptoms all over the body
40
how are the heterozygotes affected by the sickle-cell allele?
- at organismal level we observe incomplete dominance - at molecular level we observe codominance causing normal and abnormal haemoglobins to be produced which later causes some haemoglobin to remain normal and some form fibres hence only some red blood cells are sickled and other are still biconcave. - this means that heterozygotes are said to have sickle-cell traits
41
why hasn't evolutionary processes lead to a decrease or disappearance in the sickle-cell allele?
- having even one sickle cell allele may reduce the symptoms of malaria due to lower parasite densities - as the malaria parasites spend a part of their life cycle in red blood cells and since some cells are sickled that leads to lower parasite densities - hence in africa being heterozygous is an advantage as malaria cases are common.
42
State 2 dominantly inherited disorders
achondroplasia and Huntington's disease
43
how does achondroplasia affect a human?
it causes dwarfism however it is not lethal
44
how does Huntington's disease affect a human?
- it is a degenerative disease of the nervous system | - once the deterioration begins it is lethal and irreversible
45
What are multifactorial disorders? provide 1 example
- diseases with a genetic component and significant environment influences - heart disease, alcoholism, mental illnesses...
46
State the 2 types of fetal testing
- amniocentesis | - Chorionic villus sampling (CVS)
47
what is karyotyping?
number and visual appearance of the chromosomes in the cell nuclei of an organism
48
Describe the process of amniocentesis
- amniotic fluid is is taken at the starting of the 15th week - undergoes centrifugation to separate fluid from fetal cells -the fluid can be biochemically/genetically tested after a few hours the fetal cells have to be cultured for a few weeks to be able to test it or obtain numbers for karyotyping
49
describe the process of CVS
- sample of chorionic villus tissue can be taken as early as 10th week by inserting a suction tube through the cervix - after doing the we have got fetal cells no need for centrifugation - after several hours the cells can be tested or karyotyped
50
What are the 2 advantages of CVS over amniocentesis?
- Karyotyping can be done only after a few hours in CVS compared to few weeks in amniocentesis - cells in CVS can be tested as early as 10th week compared to the 15th week in amniocentesis
51
what does Phenylketonuria (PKU) cause?
- Individuals with this disorder cannot metabolise the amino acid phenylalanine causing toxic levels in the blood. - this leads to mental retardation

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