recapping chromosomes. what is a eukaryotic chromosome? chromosomes are lengths of _____ wound...
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Recapping CHROMOSOMES
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What is a Eukaryotic Chromosome?
• Chromosomes are lengths of _____ wound around protein (histone).
• Each chromosome contains many genes in a set order.
• Chromosomes are found in identical pairs (homologous pairs) in the ______ of each cell.
• One of each pair came from ____ and one from ____.
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Homeobox genes - Starter• Homeobox genes control the development of the
_____ _____ of an organism, including the ______ and positioning of the ______.
• In Drosophila, which genes determine polarity?• determine segment polarity?• determine segment identification and
development?• How many base pairs in a homeobox?• How do some homeobox genes called transcription
factors work?• Drosophila has 2 Hox Clusters of homeobox genes,
activated from head to tail of the embryo. How many do i) Nematodes and ii) Vertebrates have?
• Retinoic acid is a morphogen – what does that do?• Vit A is stored in mammalian livers. Suggest why
pregnant women are advised not to eat liver.
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AIMS• Go through Test on Tuesday• Collect exam question booklets• Chromosomes• Meiosis – work through in pairs with
plasticine and beads whilst I see everyone else about resits.
• Homework – Complete pages 9 – 14 in Meiosis booklet.
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Task - Pair and Share
• Draw a chromosome before and after DNA Replication.
• Label where appropriate:-• Genes / centromere / chromatid.• Each gene codes for the expression
of a set characteristic.• Alleles are different forms of each
gene, e.g. for tongue rolling or not tongue rolling.
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Chromosome number is fixed.
• e.g. Horse 64• Rice 12• Mouse 40• Sunflower 34• Human ?
• What do you notice about these numbers?• What would their haploid numbers be?
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Here are all 46 of our chromosomes.
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Diploid / Haploid
• Most animals and many plants have diploid somatic cells and haploid gametes.
• Haploid can be represented as n.• Diploid is then represented as __.• If n = 35 in a camel, how many
chromosomes are there in i) a somatic cell and ii) a gamete?
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Homologous pairs
• Draw an annotated homologous pair of chromosomes.
• Key points / labels• Structure / centromere / gene
sequence / gene locus (loci) / alleles / homozygous / heterozygous
• Define locus, allele, homozygous, heterozygous (if not already done) and genome.
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AIMS - http://www.youtube.com/watch?v=eaf4j19_3Zg
• Promonitor Test on Protein Synthesis, Mutations, Lac Operon, Homeobox Genes and Apoptosis tomorrow (Thursday).
• Today we shall complete Meiosis.
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And so to Meiosis. Starter from Ryan,
Chelsea, Becky and Kelly.
• Meiosis is reduction division - ……………• Meiosis produces __________.• http://www.cellsalive.com/meiosis.htm
• Now work through the Meiosis booklet and animations. Each person will need a plasticine chromosome, replicated into chromatids and with the same 2 coloured beads on one end, but of a different colour to their partner’s.
• http://www.youtube.com/watch?v=kVMb4Js99tA&NR=1&feature=endscreen
• http://www.youtube.com/watch?v=eaf4j19_3Zg Meiosis square dance• http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter12/
animations.html#
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Meiosis cut and stick
• Check up to page 8, then pages 9 and 10.
• See next few slides about mutations in meiosis.
• http://www.youtube.com/watch?v=eaf4j19_3Zg Meiosis square dance
• http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter12/animations.html#
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Chromosome Mutations
• Can you see what happens when a deletion, inversion, and translocation occur?
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Non-disjunction at metaphase 1
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Now complete page 10, then check pages 11 – 14.Research physical effects of abnormalities in number of sex chromosomes if there is time.
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AIMShttp://www.youtube.com/watch?v=eaf4j19_3Zg Meiosis square dance
• Collect in questions/tasks page 11 – 14 in Meiosis booklet for me to mark.
• Recap sources of variation – can you name four? http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter12/animations.html#
• Give back promoniter test 5• Chromosome mutations – briefly.• Check Genetics homework - Use text books page
122 onwards and slides 24 – 26 on emailed pp to complete pages 1 – 5 of “Genetics” booklet.
• Codominance.• Dihybrid Crosses.
Homework – Question 5, 6, 7 , 8a) and b)Also, more co-dominance, more dihybridquestions and stretch and challenge p 127.
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GENETICS AT A2
TOPICS TO BE COVERED
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• Genetics Terminology• Monohybrid Crosses (as done at school)• Codominance• Dihybrid Crosses• Inheritance of Sex-linked Alleles• Epistasis• Testing the Significance of the
Outcomes of Breeding Programmes by the Chi ² Test
• Continuous and discontinuous variation
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Terminology
• GENE – a length of ____ that codes for the production of a ___________ molecule.
• GENETIC CODE – • ALLELES – different forms of one
gene, e.g………………• LOCUS – the position of a gene on
a _______________ and on its homologous partner.
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• GENOTYPE – the 2 alleles which an organism possesses for a particular gene, e.g. CC, Cc or cc.
• PHENOTYPE – the expression of the genotype e.g. a person either has cystic fibrosis or not.
• DOMINANT – only one of this allele needs to be present for the allele to be ______________ in the p_________.
• RECESSIVE – two of these alleles need to be present for…………..
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CODOMINANCE – both alleles are equally dominant and so both expressed in the _____________.
So both C R (red pigment) and C W (white pigment) are expressed if together in a genotype.
The phenotype will therefore be………..
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And finally…….
• LINKAGE - 2 or more genes are located (linked) on the same chromosome.
Tall plant
Smooth seed
Linkage reduces the possible combinations of genes during meiosis and therefore reduces thephenotypes resulting from a cross.
So, no ____________ ______________ at ___________ __
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Gregor Mendel
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Pea Breeding Programmes
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An example of?
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AIMS http://www.youtube.com/watch?v=we9_CdNPuJg&feature=related
• Monohybrid starter• Check homework questions page 4• Codominance• Dihybrid Inheritance• Sex – linkage if time • Homework – page 5 of booklet,
question 4, 5, 6 and 7 on sheet + active revision for test on Wednesday.
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Monohybrid crosses
• Monohybrid crosses only take account of one feature, controlled by one gene at one locus on a chromosome.
• Genetic diagrams (Punnett squares) are used to show predicted genotypes of offspring.
• Use the accepted system for showing dominant and recessive alleles.
• Work through the examples on the next slide and then continue on page 4 and 5.
Easy!
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Remember…• Monohybrid crosses – 2 alleles
(letters) in the genotypes but only 1 in the gametes.
R R
r
r
Always ask first:
What are the genotypes of the parents?
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Monohybrid cross examples - starter
• Cystic fibrosis is caused by a faulty protein produced by a recessive allele c.
• The normal allele for the protein is C (dominant).1. Draw diagrams to show the offspring probabilities when: a) a woman with the condition has children with a healthy
homozygous man. All children are Cc so are carriers.b) Heterozygote parents have children. 1:2:1, CC, Cc, cc, so 1 in 4 chance of cf.2. A woman with genotype CC has children: 50% are ‘carriers’ Cc What is the genotype of the father? Cc – now check pages 4 and 5 in booklet.
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Genetics continued• http://www.youtube.com/watch?v=f_3Utmj4RPU
• http://www.youtube.com/watch?v=we9_CdNPuJg&feature=related
• Codominance page 6 and 7
Fainting goats!
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What are their codominant genotypes?
See question 1, page 6