Chapter 12: Sex Linkage and Polygenic Inheritance Higher Human Biology Unit 1: Cell Function and Inheritance 25/10/20151Mrs 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 25/10/20152Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

The language – Lots /10/2015Mrs 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 25/10/20154Mrs 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 25/10/20155Mrs 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. 25/10/20156Mrs 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. 25/10/20157Mrs 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. 25/10/20158Mrs 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 25/10/20159Mrs 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) 25/10/201510Mrs 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. 25/10/201511Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

Five possible genotypes for normal and red-green colour blindness GenotypePhenotype XCXCXCXC Female with normal colour vision XCXcXCXc Female (carrier) with normal colour vision. XcXcXcXc Female with colour blindness (very rare e.g. 0.5%) XCYXCYMale with normal colour vision XcYXcYMale with colour blindness more common (8%) 25/10/201512Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

Work out the genotypes of the following family tree 25/10/201513Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

Answers Carrier mother X C X c Nomal father X C Y Normal daughter X C X C Carrier daughter X C X c Normal son X C Y Colour-blind son X c Y 25/10/201514Mrs 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. 25/10/201515Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

Colour blindness problem set zona.edu/human_bio/p roblem_sets/color_blin dness/01q.html 25/10/201516Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

Puzzle 1 25/10/201517Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

Puzzle 1 - Answer 25/10/201518Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

Puzzle 2 25/10/201519Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

Puzzle 2 - Answer 25/10/201520Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

Puzzle 3 25/10/201521Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

Answer: Puzzle 3 25/10/201522Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

Puzzle 4 25/10/201523Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

Puzzle 4 - Answer 25/10/201524Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

Puzzle 5 25/10/201525Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

Puzzle 5 - Answer 25/10/201526Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

Puzzle 6 25/10/201527Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

Answer puzzle 6 25/10/201528Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

Puzzle 7 25/10/201529Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

Puzzle 7 - Answer 25/10/201530Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

Puzzle 8 25/10/201531Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

Puzzle 8 - Answer 25/10/201532Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

Puzzle 9 25/10/201533Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

Puzzle 9 - answer 25/10/201534Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

Puzzle 10 25/10/201535Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

Puzzle 10 - Answer 25/10/201536Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

Puzzle 11 25/10/201537Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

Puzzle 11 Answer 25/10/201538Mrs 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. 25/10/201539Mrs 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 (X h )is recessive to the normal allele (X H ). Hence is sex-linked. 25/10/201540Mrs 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. 25/10/201541Mrs 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. 25/10/201542Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

When the father is normal and the mother is an unaffected carrier 25/10/201543Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

Family Tree of Haemophilia 25/10/201544Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

Puzzle 1 25/10/201545Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

Puzzle 1- Answer 25/10/201546Mrs 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. 25/10/201547Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

Family Tree of Muscular Dystrophy In this family the allele survives from female carrier to female carrier. 25/10/201548Mrs 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) 25/10/201549Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

Task: Torrance pg 91 Qu’s /10/201550Mrs 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. 25/10/201551Mrs 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. 25/10/201552Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

25/10/201553Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

25/10/201554Mrs 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. 25/10/201555Mrs 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. 25/10/201556Mrs 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. 25/10/201557Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

Task: Torrance pg 93 Qu’s /10/201558Mrs 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) 25/10/2015Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance 59