Chapter 14 genetic screening and counselling
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Higher Human Biology . Unit 1: Cell Function and Inheritance. Chapter 14: Genetic Screening and Counselling. Learning Intentions. By the end of this lesson you should be able to- describe Genetic screening and counselling . Explain the use of family histories in determining genotypes.

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Chapter 14: Genetic Screening and Counselling.

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Chapter 14 genetic screening and counselling

Higher Human Biology

Unit 1: Cell Function and Inheritance

Chapter 14: Genetic Screening and Counselling.

Mrs Smith: Ch14: Genetic Screening and Councilling


Learning intentions

Learning Intentions

  • By the end of this lesson you should be able to-

    • describe Genetic screening and counselling.

    • Explain the use of family histories in determining genotypes.

      • Examples might include albinism, Huntington’s chorea, cystic fibrosis, phenylketonuria, haemophilia and muscular dystrophy.

    • Explain the use of karyotypes of foetal material where there is a possibility of genetic disorder.

    • Discuss risk evaluation in cases of polygenic inheritance.

    • Understand post-natal screening for conditions which have a genetic basis.

Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities


You need to know these words

You need to know these words

PKU

Klinefelter’s Syndrome

Genetic Screening

Councilling

Pedigree

Autosomal dominant Inheritance

Haemophilia

Sex-linked recessive trait

Prenatal

Autosomal Recessive inheritance

Post-natal

Cystic fibrosis

Chorionic villus

sampling

Huntingtons Chorea

Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities

Risk Evaluation

Amniocentesis


Use of family histories

Use of Family Histories

  • A pattern of human inheritance can be revealed by collecting information about a particular characteristic from the members of a family and then using it to construct a family tree (pedigree)

Mrs Smith: Ch14: Genetic Screening and Councilling


Types of pedigree

Types of pedigree

  • There are 3 types of pedigree that you need to know about

    • Autosomal recessive inheritance

    • Autosomal dominant inheritance

    • Sex-linked recessive trait.

Mrs Smith: Ch14: Genetic Screening and Councilling


The geneticist recognises autosomal recessive inheritance because

The Geneticist recognises Autosomal Recessive Inheritance because....

  • The trait is rarely expressed

  • The trait tends to skip generations

  • The trait is expressed in some cousins

  • Males and females are equally affected

  • All sufferers of the trait are homozygous recessive

  • Non-sufferers are homozygous dominant or heterozygous.

Mrs Smith: Ch14: Genetic Screening and Councilling


Autosomal recessive inheritance e g cystic fibrosis

Autosomal recessive inheritancee.g Cystic Fibrosis

Mrs Smith: Ch14: Genetic Screening and Councilling


The geneticist recognises autosomal dominant inheritance because

The Geneticist recognises Autosomal Dominant Inheritance because....

  • The trait appears in every generation.

  • Each sufferer has an affected parent.

  • When a branch of the family does not express the trait it fails to reappear in future generations of that branch.

  • Males and females are equally affected.

  • All non-sufferers are homozygous.

  • Sufferers are homozygous dominant or heterozygous.

Mrs Smith: Ch14: Genetic Screening and Councilling


Autosomal dominant inheritance e g huntington s chorea

Autosomal Dominant Inheritancee.g. Huntington’s Chorea

Mrs Smith: Ch14: Genetic Screening and Councilling


The geneticist recognises sex linked recessive because

The Geneticist recognises Sex-linked recessive because.....

  • More males are affected than females

  • None of the sons of an affected male show the trait

  • Some grandsons of affected males show the trait

  • All sufferers of the trait are homozygous recessive

  • Non-sufferers are homozygous dominantor or heterozygous carrier females

Mrs Smith: Ch14: Genetic Screening and Councilling


Sex linked recessive trait e g haemophilia

Sex-linked recessive traite.g. haemophilia

Mrs Smith: Ch14: Genetic Screening and Councilling


Sex linked recessive trait e g haemophilia1

Sex-linked recessive traite.g. haemophilia

Mrs Smith: Ch14: Genetic Screening and Councilling


Fyi genetic code

FYI - Genetic code

  • In 1966, the Genetic code was discovered

  • Human Genome Project to determine nucleotide sequence of human DNA began in 1990 and was completed in 2003.

  • Scientists are now able to predict characteristics by studying DNA. This leads to genetic engineering, genetic counseling.

Mrs Smith: Ch14: Genetic Screening and Councilling


Genetic code

Genetic code

An international team of scientists began the project to map the human genome.

Mrs Smith: Ch14: Genetic Screening and Councilling


Genetic code1

Genetic Code

Mrs Smith: Ch14: Genetic Screening and Councilling


Genetic code2

Genetic Code

In 1990, gene therapy was used on patients for the first time

Mrs Smith: Ch14: Genetic Screening and Councilling


Assessing the risk

Assessing the risk!

  • Once the genetic councillor has constructed the family tree(s) and established as many genotypes as possible, he/she is in a position to assess the risk and state the possibilities.

Mrs Smith: Ch14: Genetic Screening and Councilling


Assessing the risk autosomal recessive e g cystic fibrosis

Assessing the risk – Autosomal recessive. e.g. cystic fibrosis

  • If a couple were considering having a family, however the female knows cystic fibrosis runs in her family but not in her partners.

  • They could approach a genetic councillor.

  • By analysing her family tree the councillor could work out there was a 2:3 chance that the female is a carrier.

  • The councillor would already know the frequency in the British population as 1:25 for carrying the heterozygous allele for CF – this is the risk of her partner being a carrier.

  • The councillor would then conclude the risk of having a child with CF as low.

Mrs Smith: Ch14: Genetic Screening and Councilling


Assessing the risk autosomal dominant e g huntington s chorea

Assessing the risk – Autosomal Dominant. e.g. Huntington’s chorea

  • Consider a brother and sister, unlike their siblings they are too young to know if they have received the harmful allele from an affected parent.

  • They could approach a genetic councillor.

  • The councillor would already know the frequency in the British population, and there is a 1:2 chance that each is heterozygous allele for HC

  • By analysing her family tree the councillor would then conclude the risk of having of each sibling suffering this debilitating disease as high.

Mrs Smith: Ch14: Genetic Screening and Councilling


Assessing the risk sex linked e g haemophilia

Assessing the risk – sex-linked. e.g. Haemophilia

  • If a couple were considering having a family, however the female knows Haemophilia runs in her family but not in her partners. She is anxious to know if she could pass the trait onto her sons.

  • They could approach a genetic councillor.

  • By analysing her family tree the councillor would note that the woman's brother and sisters son her nephew have developed this sex linked trait.

  • This shows her sister and mother are carriers.

  • The councillor would then conclude a she has a 1:2 risk of being carrier and a 1:4 risk that each son will be a haemophiliac.

Mrs Smith: Ch14: Genetic Screening and Councilling


Advantage and disadvantagr of genetic counselling

Advantage and disadvantagr of Genetic counselling

  • The aim of genetic counselling is to help people to make well informed decisions for themselves based on information available.

  • Advantage: Analysis of a family tree allows the expert to chart he pattern of the disorder.

  • Disadvantage: It is of limited value in that it can only offer an assessment of risk.

Mrs Smith: Ch14: Genetic Screening and Councilling


Pre natal screening

Pre-natal Screening

  • If after assessing the risk of having baby with a genetic disorder. AND IF the couple decide to go ahead and have a baby pre-natal screening can be employed.

  • Two methods of pre-natal screening depend on foetal material being obtained to allow karyotypes to be examined

    • Amniocentesis

    • Chorionic villus sampling (CVS)

Mrs Smith: Ch14: Genetic Screening and Councilling


Amniocentesis

Amniocentesis

  • Amniocentesis is carried out in the 18th week of pregnancy.

  • It involves the withdrawal of a little amniotic fluid containing foetal cells.

  • These cells can be analysed and a full karotype made.

  • It slightly increases risk of miscarriage


Chorionic villus sampling

Chorionic Villus Sampling

  • A small tube is inserted into the womans reproductive tract, placental cells are removed, these cells are used for karyotyping

  • ADV: CVS can be carried out at 8 weeks of pregnancy

  • DISADV: Causes a higher risk of miscarriage then amniocentesis


Post natal screening

Post-natal Screening

  • At present none of the inherited disorders can be successfully treated except for PKU

  • Phenylketonuria results from an inborn error of metabolism for 1:10000 b irths in Britain.

  • If not detected soon after birth the baby suffers from mental retardation

  • All British babies are routinely tested for excess phenylalanine after birth by means of a blood test

Mrs Smith: Ch14: Genetic Screening and Councilling


Testing for pku guthrie s test

Testing for PKU: Guthrie's test

Mrs Smith: Ch14: Genetic Screening and Councilling


Task tyk torrance pg106 qu s 1 3

Task: TYK -Torrance pg106 Qu’s 1-3

Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities


Task ayk torrance pg 106 7 qu s 1 4

Task: AYK -Torrance pg 106-7 Qu’s 1-4

Applying your knowledge

Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities


Essay question guide to h grade essays pg 64

Essay Question Guide to H-Grade essays pg 64

By means o examples you have studied discuss genetic conditions of medical importance with reference to the following:

  • Family History

  • Use of Karyotypes

  • Post-natal Screening.

    (15)

Mrs Smith


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