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Gregor Mendel - 3.11B
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Genetic Variation
In this course, Dr Matt Ivory (Cardiff University) introduces genetic variation, covering topics 3.11B-3.17B, 3.19 and 3.20 in the Pearson Edexcel GCSE Biology (9-1) Specification for Foundation Tier. We begin by: (i) describing the work of Gregor Mendel and his work to understand variation and inheritance in pea plants (Topic 3.11B); and (ii) explain why there are differences in the inherited characteristics as a result of alleles, explaining key terms in the field (Topic 3.12, 3.13); before (iii) discussing describing and practising monohybrid inheritance using different representations (Topic 3.14, 3.16); before (iv) understanding some complexities of sex-linked inheritance and codominance (Topic 3.15, 3.17B, 3.19); and finally (v) take a look at the ways that phenotype can vary as a result of genetic and environmental variation (Topic 3.20).
Gregor Mendel - 3.11B
In the first mini-lecture, we discuss the history of our understanding of inheritance, as brought up in topics 3.11B of the Pearson Edexcel GCSE (9-1) Biology specification. We describe Gregor Mendel, a monk from the 19th century, and his work discovering the basis of genetics and recognise the difficulties of understanding inheritance before the mechanism was discovered. We analyse his work with pea plants with different characteristics, including plant height, flower colour, seed colour and seed shape to uncover genes and alleles, the genetic code responsible for these traits. To finish off, we learn about what Mendel concluded from this research by looking at his three laws of inheritance.
Hi, My name is Dr Matt Ivory.
00:00:06I'm a lecturer in the School of
00:00:07Pharmacy and Pharmaceutical Sciences in Cardiff University.
00:00:08And in this series of talks,
00:00:12we're going to dig down a bit into the history of genetics and inheritance.
00:00:13Look at some of the early work in that field,
00:00:17and we'll look at how we can calculate inheritance based on the genotype of parents.
00:00:19So Gregor Mendel was a monk who lived from 18 20 to 18 84
00:00:25and because of the work that he did, he is known as the father of modern genetics.
00:00:30So prior to the work that he did,
00:00:35people believed that traits of a child were a
00:00:37blend of the traits from the two parents.
00:00:41So if you had a parent with very fair skin
00:00:43and a parent with very dark skin,
00:00:47that the offspring would all be kind of medium skin tone
00:00:49and height as well.
00:00:54So if it was a very tall father, a very short mother,
00:00:56you'd produce a child that was of medium height.
00:00:58But this didn't actually hold true with a number of different traits,
00:01:01so to parents with brown hair would sometimes have Children with red hair.
00:01:05And so obviously the middle point of two parents with brown hair isn't red hair,
00:01:10and so something else was going on.
00:01:16So the work that Mendell did involved pea plants
00:01:18and he did this in his monastery,
00:01:23and this laid the foundations for the mechanisms of inheritance.
00:01:25And from that, the field of genetics has grown
00:01:31so practically. The work that Mendell did was he took some P plants
00:01:35and he used a paintbrush to cross pollinate plants so
00:01:41he'd take pollen from one plant using his paintbrush,
00:01:45and he'd apply it to a different plant.
00:01:48And in that way he could carefully control
00:01:51which plant was pollinated by another plant.
00:01:54He would then seal off the pollinated plant to make
00:01:58sure that it wasn't pollinated by any other individual plants.
00:02:00And so he could be 100% sure that the
00:02:04offspring that were produced with the result of the plant
00:02:07that he took the pollen from and the plant that he put the pollen on to pollinate it.
00:02:09And so he carefully bred plants with different characteristics
00:02:15and combined them to see how these characteristics will be passed on.
00:02:19So some of the things that he looked at where the height of the plant,
00:02:24the colour of the flowers, the seed colour and the seed shape, amongst other things.
00:02:28So what he found was that when he took a tall plant and a dwarf pea plant
00:02:33and cross pollinated them that all of the offspring were tall pea plants,
00:02:39and when he took two of these P plants that
00:02:46he'd produced from the tall one and the dwarf one
00:02:48and crossed them with each other,
00:02:51the offspring would consist of three tall P plants
00:02:53and one dwarf pea plant.
00:02:56So from this,
00:02:58he concluded that there was some factor that
00:02:59was controlling the inheritance of these traits,
00:03:01and that these factors didn't change throughout the life of the plants.
00:03:04It wouldn't be that a young plant would be more
00:03:07likely to produce a tall plant or a dwarf plant.
00:03:09It was fixed throughout the life of the plant,
00:03:11and these are what we now call al eels of a gene. So there's more on genes and alleles.
00:03:14In the next talk, we'll talk through it in a bit more detail,
00:03:20but it's a very important discovery to work out how characteristics were passed on,
00:03:24and he summarised his work into three laws of inheritance.
00:03:30So the first law of inheritance is that characteristics implants
00:03:34are determined by the factor what he called a factor,
00:03:38what we now call al eels contained within the gametes.
00:03:41So one is obtained from each parent. So in plants, the pollen is the male gamete,
00:03:44whereas in humans it's sperm cells and egg cells. So different cells.
00:03:50But each of them will have half the genetic material needed
00:03:55and will produce offspring with half of the genetic material from each parent.
00:03:59So the second law is that the version of
00:04:05the alley or received from each parent is random,
00:04:07and versions of valuables don't change, so you can't blend them
00:04:10together so they are unchangeable.
00:04:14And last but not least,
00:04:17the third law is that there are dominant and recessive versions of valuables,
00:04:18so if you have one of each, the dominant factor will always dictate the
00:04:22type of the offspring.
00:04:27So it wasn't until after he died that we developed more
00:04:28nuanced techniques to work out the true mechanism for inheritance,
00:04:33but with the tools that he had available to him.
00:04:38This was very groundbreaking work and helped pave
00:04:40the way for these more kind of complex,
00:04:43um, investigations to uncover the genetic molecular basis for inheritance.
00:04:46So unfortunately, there were some limitations to the work,
00:04:53so it wasn't particularly well communicated at the time that he did it,
00:04:56and he didn't publish it very widely. And so the initial impact was quite limited.
00:05:03Um, it also only worked for characteristics that are controlled by a single gene,
00:05:08and those were only two alleles exist.
00:05:14So the tall and dwarf jeans it's only one
00:05:16gene that determines the height of the P plant.
00:05:21And there's only two available valuables,
00:05:23so the gene is either at all or it's for dwarf,
00:05:25so there's lots of characteristics in organisms that
00:05:29involve the some effect of many genes.
00:05:32Some of them involve environmental input as well,
00:05:35and there's also lots of genes that have more than two a leal's.
00:05:38So the picture becomes a little bit more complicated
00:05:42when you move into those more complex situations.
00:05:44And there was some pushback by the scientific community as well,
00:05:49because the unchanging nature of valuables, according to Mendel,
00:05:51was in conflict with Charles Darwin's work around the constant change and the
00:05:55increase in genetic diversity that allowed for
00:06:02evolution by survival of the fittest.
00:06:05So if all of the illegals stayed constant forever, there'd be no evolution,
00:06:07and all organisms would remain exactly the same.
00:06:12
Cite this Lecture
APA style
Ivory, M. (2022, November 22). Genetic Variation - Gregor Mendel - 3.11B [Video]. MASSOLIT. https://massolit.io/courses/genetic-variation-pearson-edexcel-gcse-9-1-biology-for-foundation-tier/genetic-and-environmental-variation-3-20-90f8768f-6b6d-4ed5-a6a1-45e76559e9f8
MLA style
Ivory, M. "Genetic Variation – Gregor Mendel - 3.11B." MASSOLIT, uploaded by MASSOLIT, 22 Nov 2022, https://massolit.io/courses/genetic-variation-pearson-edexcel-gcse-9-1-biology-for-foundation-tier/genetic-and-environmental-variation-3-20-90f8768f-6b6d-4ed5-a6a1-45e76559e9f8