Chapter 12: Sex Linkage and Polygenic Inheritance Higher Human Biology Unit 1: Cell Function and...
-
Upload
claud-lawrence -
Category
Documents
-
view
230 -
download
0
Transcript of Chapter 12: Sex Linkage and Polygenic Inheritance Higher Human Biology Unit 1: Cell Function and...
Chapter 12: Sex Linkage and Polygenic Inheritance
Higher Human Biology
Unit 1: Cell Function and Inheritance
20/04/23 1Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
Learning intentions;
• To revise sex chromosomes
• To examine effects of sex-linked genes
• To look at polygenic inheritance
20/04/23 2Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
The language – Lots........
20/04/23 Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
3
The stuff you Need to know!
• Sex-linked inheritance and the effects of the presence of genes on the X-chromosome and not on the Y-chromosome.
• Polygenic inheritance leading to characteristics
20/04/23 4Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
Normal Body Cells
• In the nucleus of every body cell there are 46 chromosomes
• 22 homologous pair (AUTOSOMES) and one pair of sex chromosomes
20/04/23 5Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
Female and Male Sex Chromosomes
• In the female, the sex chromosomes make up a fully homologous pair, the X chromosomes.
• In the male, the sex chromosomes make up a pair consisting of an X and a much smaller Y, which is homologous to only part of the X chromosome.
20/04/23 6Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
Sex-linked genes.
• The X and Y chromosomes behave as a homologous pair at meiosis. However, the X
chromosome differs from the Y chromosome in that the larger X carries many genes not present on the smaller Y. These genes are said to be sex-linked.
20/04/23 7Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
At fertilisation• When an X chromosome meets a
Y chromosome at fertilisation, each sex-linked gene on the X chromosome becomes expressed in the phenotype of the human male produced.
• This is because his Y chromosome does not possess alleles of any of these sex-linked genes and cannot offer dominance to them.
20/04/23 8Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
Symbols
• In crosses and family trees involving sex-linked gees, the sex chromosomes are represented by the symbols X and Y and the alleles of the sex-linked gene by appropriate superscripts.
Sex-linked genes
20/04/23 9Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
X-linked recessive disorder - Red Green Colour Blindness
• Inability to distinguish between red and green• A red green colour blind person does not see the
number 29 on the right• In humans normal vision (C) is completely
dominant to red-green colour blindness (c)
20/04/23 10Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
Genetics of Colour Blindness
• Normal vision C
• Red-green colour blindness c
• These are the alleles are sex-linked because...
• Heterozygous females are called carriers (Cc)
Although they are unaffected themselves there is a 1 in 2 chance (50%) chance that they will pass the allele on to each of the offspring.
20/04/23 11Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
Five possible genotypes for normal and red-green colour blindness
Genotype PhenotypeXCXC Female with normal colour vision
XCXc Female (carrier) with normal colour vision.
XcXc Female with colour blindness (very rare e.g. 0.5%)
XCY Male with normal colour vision
XcY Male with colour blindness more common (8%)
20/04/23 12Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
Work out the genotypes of the following family tree
20/04/23 13Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
Answers
• Carrier mother XCXc
• Nomal father XCY
• Normal daughter XCXC
• Carrier daughter XCXc
• Normal son XCY
• Colour-blind son XcY20/04/23 14Mrs Smith: Ch12 Sex Linkage and
Polygenic Inheritance
Why is colour blindness more common in males?
• Red green colour blindness is rare in females since 2 recessive alleles must be inherited.
• It is more common in males where only one is needed.
20/04/23 15Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
Colour blindness problem sethttp://www.biology.arizona.edu/human_bio/problem_sets/color_blindness/01q.html
20/04/23 16Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
Puzzle 1
20/04/23 17Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
Puzzle 1 - Answer
20/04/23 18Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
Puzzle 2
20/04/23 19Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
Puzzle 2 - Answer
20/04/23 20Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
Puzzle 3
20/04/23 21Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
Answer: Puzzle 3
20/04/23 22Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
Puzzle 4
20/04/23 23Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
Puzzle 4 - Answer
20/04/23 24Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
Puzzle 5
20/04/23 25Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
Puzzle 5 - Answer
20/04/23 26Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
Puzzle 6
20/04/23 27Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
Answer puzzle 6
20/04/23 28Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
Puzzle 7
20/04/23 29Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
Puzzle 7 - Answer
20/04/23 30Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
Puzzle 8
20/04/23 31Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
Puzzle 8 - Answer
20/04/23 32Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
Puzzle 9
20/04/23 33Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
Puzzle 9 - answer
20/04/23 34Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
Puzzle 10
20/04/23 35Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
Puzzle 10 - Answer
20/04/23 36Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
Puzzle 11
20/04/23 37Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
Puzzle 11 Answer
20/04/23 38Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
Haemophilia: mutated form of factor VIII in platelets
• Haemophiliacs cannot make the blood clotting protein Factor VIII.
• This is a problem with blood clotting. So, if a tissue is damaged and blood vessels are broken, bleeding continues for longer than normal.
• Some bleeding is obvious such as when the skin is cut or broken. Others are less easy to spot like bleeding into or around the joints.
20/04/23 39Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
X-linked recessive disorder -Haemophilia
• It caused by a recessive allele carried on the X (e.g. The gene is located on the non-homologous region of the x-chromosome) but not the Y chromosome.
• The haemophiliac allele (Xh)is recessive to the normal allele (XH).
• Hence is sex-linked.
20/04/23 40Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
More common in males than females
• Haemophilia is more common in men than women.• Fequency in britian is 1:5000• Males inherit the allele from their mother and develop
the disease.• Since (until recently) the prognosis for survival was
poor and haemophiliac males did not survive to pass on the allele to their daughters (its on the X-chromosome). Therefore females with haemophilia where rare.
20/04/23 41Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
There is now treatment -FYI
• ‘Clotting factor concentrates’ revolutionised haemophilia care allowing patients to travel, have jobs, and live full and independent lives.
• Transfusion with whole blood and plasma.
20/04/23 42Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
When the father is normal and the mother is an unaffected carrier
20/04/23 43Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
Family Tree of Haemophilia
20/04/23 44Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
Puzzle 1
20/04/23 45Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
Puzzle 1- Answer
20/04/23 46Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
Muscular Dystrophy• Duchenne Muscular Dystrophy is the
most common form of this disease.• Sufferers are severely disabled from an
early age.• The normally die without passing allele
onto the next generation.• Afects 1:3000 male infants.• Skeletal muscles loose their normal
structure and fibrous tissue develops in their place.
• Caused by a recessive allele carried on the X chromosome and is sex-linked.
20/04/23 47Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
Family Tree of Muscular Dystrophy
• In this family the allele survives from female carrier to female carrier.
20/04/23 48Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
Polygenic Inheritance
• Polygenic inheritance is a characteristic showing continuous variation and is controlled by the alleles of more than one gene
• The more genes involved the more intermediate phenotypes that can be produced
• The effects of the genes are additive (each dominant allele of each gene adds a contribution towards the characteristic controlled by the gene)
20/04/23 49Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
Task: Torrance pg 91 Qu’s 1-3
20/04/23 50Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
Polygenic Inheritance -Discontinuous Variation.
• A characteristic shows DISCONTINUOUS VARIATION if it can be used to divide up the members of a species into two distinct groups.
• e.g. Can roll tongue vs Cannot roll tongue.
• Such information is often presented in a bar chart.
20/04/23 51Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
Polygenic Inheritance -Continuous Variation.
• A characteristic shows CONTINUOUS VARIATION when it varies amongst the members of a species in a smooth continuous way from one extreme to another, and does not fall into distinct groups.
• e.g. Height – varies from very small to very tall. Also, skin colour, weight
• Such information is often presented in a HISTOGRAM.
20/04/23 52Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
20/04/23 53Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
20/04/23 54Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
The additive effect of polygenic genes• The genes involved in polygenic
inheritance are transmitted from generation to generation via meiosis in the normal way.
• What makes them different from other genes is that their effects are ADDITIVE. That is each dominant allele of each gene adds a contribution towards the characteristic controlled by the genes.
20/04/23 55Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
Effect of Environment
• Many of these characteristics are influenced by the environment.
• Polygenic inheritance + environmental factors = phenotypic characteristic which shows a wide range of continuous variation and a normal pattern of distribution.
20/04/23 56Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
Many characteristics which show continuous variation (e.g. Height, foot size, etc.) are
influenced by the environment
• They are dependant on favourable environmental conditions for their full phenotypic expression.
• For example, regardless of how many dominant alleles for height that a person inherits, he or she will not reach their full potential for height without consuming an adequate diet during childhood and adulthood.
20/04/23 57Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
Task: Torrance pg 93 Qu’s 1+2
20/04/23 58Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
Essay Question Guide to H-Grade essays pg 60
With named examples, discuss how inheritance of sex linked traits differ from that of autosomal traits. (15)
20/04/23 Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance
59